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Atlas Copco Underground Construction

UNDERGROUND CONSTRUCTION

COMMITTED TO SUSTAINABLE PRODUCTIVITY

Printed matter no. 9851 3427 01

www.atlascopco.com

A global review of tunneling and subsurface installations

2015

We stand by our responsibilities towards our customers, towards the environment and the people around us. We make performance stand the test of time. This is what we call – Sustainable Productivity.

FIRST EDITION 2015

Contents

5

Foreword

7

Talking Technically

205

Case Studies

4

ATLAS COPCO MINING METHODS

Welcome to the

world of tunneling As global urbanization gains unprecedented momentum, tunneling expertise and rock excavation technology are playing a crucial role in shaping the future of our societies. Simply put, going underground is rapidly becoming the only viable option for meeting the infrastructure needs of the 21st century. According to UN estimations, 7 out of 10 people will be living in cities by 2050, meaning that a further 2.5 billion people will be added to the world's urban populations. The new city dwellers will all be dependent on the utilities and services that many of us take for granted: integrated transportation systems for road and rail, sufficient freshwater supplies, reliable sources of energy, functioning sewage and storm surge systems, to mention just a few examples of where tunnels provide key solutions.

“

Tunnels are the only option for tomorrow’s urban society.

”

What’s more, rules and regulations governing underground construction will only become stricter. Tunnels will need to be built and upgraded in the most environmentally sustainable, safe, responsible and economical way. It is a difficult challenge but one that an increasing number of tunneling professionals are conquering with groundbreaking results. Not only that, due to the demands of urbanization these tunnel designs are becoming increasingly complex. In this technical reference book, we turn a spotlight on the most common methods and practices in tunnel engineering – the backbone of all underground construction. As a leading supplier of rock excavation equipment for more than 140 years, Atlas Copco presents a holistic perspective of the industry, exploring a wide range of issues from market development, safety and operator training to environmental care and the role of technology and innovation. Whatever area of the industry you are working in or planning to join, we trust you will find this first edition of Underground Construction a valuable source of information and inspiration.

Sincerely, The Editorial and Application Specialists Team Atlas Copco Underground Rock Excavation

SAFETY FIRST Atlas Copco is committed to comply with or exceed all global or local rules and regulations for personal safety. However, some photographs in this reference book may show circumstances that are beyond our control. All users of Atlas Copco equipment are urged to think safety first and always use proper ear, eye, head and other protective equipment as required to minimize the risk of personal injury.

REFERENCE BOOK

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ATLAS COPCO UNDERGROUND CONSTRUCTION – TALKING TECHNICALLY

Talking technically Tunneling overview 8 Tunnel excavation: A look back in history 18 The role of tunnels: Global market overview

Rock classification 26 Geology and why it matters 36 Geotechnical investigations 42 Rock mechanics

The tunneling process 48 52 56 58 62 66

Planning for new tunnels Management of projects Operator training and simulators Worksite infrastructure Maintenance Remote monitoring

Underground construction 68 Road and rail tunnels 80 90 98 104

Hydroelectric power plants Water and utility tunnels Oil and gas caverns Utilization of underground space

110 Radioactive waste deposits

Tunneling technique 116 Ventilation systems: Optimizing the air flow 120 130 138 144 150 158 164 170 174

High precision drilling Charging and blasting Data management tools The raiseboring complement Rock reinforcement Loading and haulage Grouting Diamond wire cutting Choice of methods

Trends in tunneling 186 Technical trends in tunneling 190 Safety 194 Energy consumption 200 Tunnel maintenance

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Tunnel excavation for civil purposes became widespread from the mid-19 th century and onwards. Using brick lining as a permanent support was standard practice and it consisted of regular bricks with filling material behind the brick arch. This created an adhesion effect between the rock wall and roof and the load bearing arch.

A rich story written in stone

Man has been working underground for more than 5 000 years, and the lessons learned over the centuries, often in the face of overwhelming odds, have shaped the modern world of tunneling. Archaeological discoveries tell us that man has been working underground since the Stone Age. In those early days some 5 000 years ago, flint miners would use deer antlers as pickaxes to hack their way through limestone in search of flint. As they became more skilled, they learned to tunnel their way to flint deposits deep in the earth and to build underground rooms that became the hubs for smaller drifts. Ancient flint mines are not the only evidence that remains of early underground workings. There are many other examples

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such as the Hallstatt salt mine in Austria that dates from 1 000 BC. Here, miners built tunnels with inclines of between 25 and 60 degrees in order to reach the salt, and then created drifts stretching as far as 400 m from the tunnel portals. Added to this are rooms measuring 12x12 m, evidence of mining operations that were carried out at depths of 100 m or more. Handheld tools were naturally used, and these were mostly bronze pickaxes with wooden handles, sledgehammers, chisels, and buckets for loading.

ATLAS COPCO UNDERGROUND CONSTRUCTION – TALKING TECHNICALLY

TUNNEL EXCAVATION: A LOOK BACK IN HISTORY

Completed in 1965, the Mont Blanc Tunnel in France proved a major success for Atlas Copco tunneling techniques. The tunnel was driven, from the Italian side, exclusively with light pusher leg fed rock drills and Coromant drill steels.

So now let’s jump forward a 1 000 years or so to the days of the Roman Empire. During this period, underground mining and construction only existed on a limited scale, and the Romans did not contribute much of any importance to the development of tunneling technique. The fire-setting method was known but not used, most likely due to the unpleasant fumes, smoke and heat that this would have caused in the already hot and stifling Mediterranean climate. The tools that were used were now made of iron, but beyond that, there was very little improvement in terms of technical development. With the exception of fire-setting, underground mining remained largely the same in most parts of the world during Roman times, right up until the 1700s when black powder, or gunpowder, came onto the scene. It was first used for blasting in Scandinavia at Nasafjäll in 1630, but in central Europe black powder was used as early as the 14th century.

William Bickford invented the encapsulated string fuse in 1830, which, when used together with black powder explosives, pioneered the safe detonation of rounds. Nitroglycerin, which was invented in the 1840s, was unpredictable, but this was solved by Alfred Nobel, who in 1865 invented a detonator that could control the ignition process. The demand for safer, more efficient rock blasting grew, and the first pneumatic rock drill was developed in 1857.

Fréjus – the start of modern tunneling

The construction of the Fréjus Tunnel that runs through the Alps between France and Italy is largely regarded as the start of modern tunneling technology. By 1870, the railway network had expanded dramatically across Europe as it had in the United States, but the mighty Alps still remained unconquered. To run a railway through the Alps would require long tunnels located deep beneath the mountains, and the technique needed to do that had not yet been mastered. It would

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Tunneling overview

The drilling of blastholes by hand is also well documented. Two operators were required, one to strike the blows while the other took care of the rotation, feed and direction. In this way, blastholes, such as those at the Falun copper mine in Sweden, were drilled to a maximum depth of 1 m. Industrialization was then catapulted into the future on the back of several remarkable inventions. The famous race between the steam

engine prototypes – George Stephenson’s “Rocket” and John Ericsson’s “Novelty” – at Rainhill in England in 1829 was the start of the big railway era, and by 1850 about 8 000 km of railway had been built in England (see map in chapter Road and rail tunnels, p.76.)

TUNNEL EXCAVATION: A LOOK BACK IN HISTORY

The Sommeillers drill rig was used at the Fréjus Rail Tunnel from 1857 to 1871. Equipped with 4–9 pneumatic drills, the rig weighed 12 tonnes and was operated by a crew of 30–40 people.

require a tunnel more than 12 km long with a rock cover of up to 1 200 m, making it impossible to use intermediate shafts for either ventilation or access. This meant that such a tunnel could only be driven from its two end portals. For the next 20 years, various tunnel planners studied how such a tunnel could be constructed – and that was also how long it took to develop the necessary technology. A water-powered compressed air unit had been invented, and the aim was to use the compressed air released by the rock drill as a fresh air supply for the workers. It didn’t work very well. Then they tried to convert a steam-powered rock drill into a pneumatic rock drilling unit, but this didn’t work well either. Nonetheless, despite many drawbacks and uncertainties, it was decided to go ahead, and the project was finally started with an estimated construction period of 20 years. The work began with a pilot tunnel of 3.3 x 2.4 m, which was then enlarged by a crew of 200 to its full cross section of 70 m2 some 25 m behind the face. The first few years were dominated by sledgehammer drilling equipment, and progress was, therefore, slow. The performance records differ slightly on this point, but the daily advance was said to be somewhere between 0.25 and 0.6 m per day. The average hole depth was recorded in the region of 0.5 to 0.9 m.

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In 1863, the first Sommeillers drilling platform was put into operation. This machine weighed 12 tonnes and was equipped with 4–9 pneumatic rock drills, flushing water tanks as well as a selection of spare parts, and it was operated by a crew of 30 to 40 people.With the introduction of this platform, the maximum advance increased to about 3 m per day during 1864, and this later increased to 4 m per day up to the breakthrough year of 1870. The drillers drilled 0.8 to 0.9 m deep holes, 30–40 mm in a diameter, and there were about 80 men at work in the pilot tunnel at any one time. More than 4 000 people were engaged in the construction of the Fréjus tunnel, and it was completed in 13 years (1870) – significantly faster than the original 20-year estimate. Due to the relocation of the portal on the French side, the total length was also increased to 13.7 km. This was clearly the instigator of a great many other tunnel projects in the Alpine region, several of which belong to the same period up until the turn of the century. The image above gives an idea of how the project was carried out. Here we can see the Sommeillers drilling platform in the pilot tunnel and the drill plan, before the tunnel was enlarged. The drill rods were 3.8 cm (1.5 in) in diameter, and three uncharged holes were drilled to form the initial opening.

ATLAS COPCO UNDERGROUND CONSTRUCTION – TALKING TECHNICALLY

TUNNEL EXCAVATION: A LOOK BACK IN HISTORY

Figure 2: Drilling on the 13.7 km long Fréjus Rail Tunnel project started in August 1857 in the Piedmont region of Italy, in the Alps. Above, an old locomotive exits the first tunnel of Fréjus near the town of Modane, on the French side.

However, it wasn’t possible to drill very far before the drill rods had to be sharpened. Reports on bit wear using jackhammers at a contemporary (1865) tunneling site in Massachusetts, USA, make interesting reading. With a tunnel length of 190 m and a cross section of 80 m 2, the drilling of some 10 000 m through mica schist and granite blunted about 150 000 chisels. This meant that the bits had to be reground after every 7 cm. There is no reason to believe that in the same type of rocks a significantly better result had been achieved at the Fréjus tunnel. As for the rock drills, these required constant repairing, and in order to keep 20 machines up and running simultaneously at the face, no less than 60 units were in the workshop at any one time undergoing repairs.

From its setup position, this rig could cover the entire face and enable the drillers to drive the tunnel in one full section operation. As tunneling advanced, the rig was moved forward and repositioned by a truck. A so-called double-front operation was employed whereby drilling and charging was carried out in one tunnel while mucking out was carried out in the other. The hole depth was just over 3 m, and with each blast, the tunnel advanced 2.7 m per round. The drilling was done by six rock drills, known as drifters. An electric excavator with a bucket capacity of 0.4 m3 was used for loading, and productivity was a good 9 m3 per hour. The average advance over a four-week period was 65 m counting both fronts, or one blast per day. 1947 to 1967 was certainly a dynamic period for drilling technology, largely due to the advent of three more technical developments: cemented carbide bits, the lightweight rock drill and the compressed air pusher leg.

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Tunneling overview

It was during this period that pneumatic drills had their biggest breakthrough, and even though cemented carbide was not available at this time, the drill steel performed significantly better during the construction of the Fréjus tunnel than in the Massachusetts project in the 1860s. This was mainly due to less wearing rock formations. Some 50 years later, at the beginning of the 20 th century, regrinding of drill bits was normally required after 50–60 cm of drilling in gneisses and granites. Fast forward another 30 years (before the introduction of tungsten carbide

bits). It is worth taking a brief look at a case study carried out between 1937 and 1939 that focuses on the construction of a streetcar tunnel in the Hammarby district outside Stockholm, Sweden. The tunnel cross section was 33.5 m 2 and comprised of two separate drives, each 400 m long. The rock was granite, the tunnels were driven from an open area between the tunnels and this This was the first time in Sweden that a so-called drill jumbo was used.

TUNNEL EXCAVATION: A LOOK BACK IN HISTORY

"The Swedish Method" had its international breakthrough in 1946 and was based on light, one-man operated rock drills equipped with pusher leg feeds.

All three did not come along at the same time, but in 1947 they were firmly established, even though it would take several years before they would be fully introduced. Tungsten carbide, which had been discovered some years earlier, was found to be highly resistant to the abrasiveness of rockbearing minerals. Scientists had also succeeded in attaching carbide inserts to the ends of steel rods by means of a special soldering process to form the cutting edges of a drill bit. A lightweight, air-powered rock drill that could be operated by one man represented another huge step forward. As indicated earlier, there were a number of similar models already in existence, but it was the smoothness of the latest models that made them truly superior. In addition, the latest pusher leg, which was also powered by compressed air, was an improvement compared to previous designs. It had a straight feed that pushed the rock drill and bit against the rock. The leg was supported from the tunnel invert. Together, these units were marketed under the name “The Light Swedish Method”. Also better drilling platforms, or jumbos as they were known, were developed that made it easier to move the handheld drills around to cover the large tunnel face areas.

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One example of how this development impacted subsequent tunneling projects is the Vinstra hydropower plant in Norway, where drilling and blasting was carried out around 1950 when the hydropower plant was expanded. The main headrace tunnel was to be a full 23 km long and had a cross section of 30 m 2, and it took the shape of a D. The project was successful and brought The Light Swedish Method its first international recognition for effectiveness and efficiency. As shown in Figure 2, the tunnel excavation began with a 13 m 2 pilot drive at the invert level with the full tunnel width. The top was then drilled in two steps. During the first shift, the pilot hole was drilled to a depth of about 2 m (7 ft), and the lower crown part, which consisted of five holes, was drilled to twice that depth, followed by blasting and mucking out. During the second shift, the pilot tunnel was drilled again, as were the remaining holes in the crown (the upper part), to twice the pilot hole depth. The crews included six men in one shift, five drillers plus a foreman, and they achieved an average advance of 25 m per week, corresponding to two rounds per day. The mobilization time for each blast was extremely short, reportedly about seven minutes, and the drill bits lasted for 15 m before regrinding was necessary. Ordinarily, the

ATLAS COPCO UNDERGROUND CONSTRUCTION – TALKING TECHNICALLY

TUNNEL EXCAVATION: A LOOK BACK IN HISTORY

rock formation at this site, which was reported as mica schist, would have been medium-hard to drill and quite difficult to blast. It was also considered remarkable that during the drilling operations the rock drill was in operation for 85% of the time. This project was later used by Atlas Diesel for marketing the Light Swedish Method. The illustration in Figure 3 shows a drill jumbo for a largesize tunnel that uses a so-called V-cut. In this case, a drill jumbo equipped with 16 feeds of so-called ladder type required eight drillers to keep all 16 fully occupied. All these different types of drill jumbos were the predecessors of what we today mean by drill rigs: a carrier with individually operated booms, each carrying a rock drill mounted on a feed. In the late 1960s, a new period in tunneling techniques developed with the arrival of heavy duty rock drills that could be mounted on drill rigs. This technology came from Ingersol Rand and Gardner Denver in the United States. This forced the Light Swedish Method into the background, although it remained in use for many years for small-size tunneling and, in fact, is still in use in many parts of the world today.

Figure 2: A blueprint of the drilling platform used to create the 30 m2 crosssection tunnel.

A drastic change of technology was soon about to take place – the introduction of the hydraulic rock drill. This invention was launched in the early 1970s and quickly won popularity among its users. These new machines gave about 25% better penetration when compared to air-driven drills at the same impact-power per blow. They could also be designed in such a way that the shock wave that was transmitted to the drill rod transferred significantly less mechanical stress to the drill steel, consequently reducing drill steel consumption. The development of drill steel technology also took a major step forward during this period with the introduction of button bits, which were a crossover from oil drilling technology using roller cone bits. The introduction of the button bit resulted in increased penetration rates of about 20%. These bits were also cheaper to produce, which helped to reduce the cost-per-meter drilled. So what effect did all these technical developments have on tunneling technology? The hydropower plant in Skibotn in northern Norway is a typical case study. The plant was built in the late 1970s and included 35 km of tunnels ranging in size from 18 m 2 to 30 m 2. They were constructed according to contractor Höyer Ellefsen’s tunneling concept, which was based on the use of rubber wheel-bound equipment and loading bays installed every 120 m along the alignment.

Figure 3: A "jumbo" drill rig equipped with hydraulic feed was used for the construction of the Inverawe hydroelectric power station in Scotland, commissioned in 1963.

ATLAS COPCO UNDERGROUND CONSTRUCTION – TALKING TECHNICALLY

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Tunneling overview

To do the job, the contractor used: • Atlas Copco’s drill rig Promec TH 470 with COP 1038 HD rock drills • A truck mounted ANFO charging unit • Caterpillar 980 loaders • Haulage trucks of 10–12 m3 capacity

TUNNEL EXCAVATION: A LOOK BACK IN HISTORY

Known as the "Fréjus Jumbo", this Promec drilling rig was developed specifically for the Fréjus Road Tunnel that runs through the Alps and connects Bardonecchia in Italy with Modane in France. It was opened in 1979.

In terms of manpower, only three men were required – two for drilling and charging and one to operate the loader, and a local firm was subcontracted to haul away the muck. The tunnelers worked a three-shift work schedule, which at that time was still acceptable in Norway, amounting to a 120 h workweek. During a two-month period in the autumn of 1977, an average of 130 m per week was achieved at two fronts. It is possible that this short period is not representative of the entire project, but it still shows what could be achieved with the equipment that was available at the time, namely 10 rounds per day, or 3.3 rounds per shift. A similar example from the same period is the Fréjus road tunnel, which runs close to the old Fréjus railway tunnel described earlier. The total tunnel length was 13 km, and it was driven from the end portals, with one in France and one in Italy. The cross section was 85 m 2. On the French side, regular drill rigs were used including two five-boom rigs and two three-boom bolting rigs. On the Italian side, however, a rig specially built for this purpose was used (see photo above).

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It was equipped with six booms and used for both blasthole drilling and bolting. Each round consisted of approximately 120 drill holes with a diameter of 51 mm. The depth of the rounds ranged between 4.3 m and 5 m. Mucking out was done with a 150 kW Bröyt digger. Drilling, charging, blasting and scaling took 4.5 h. Mucking, bolting and other reinforcement work took 6.5 h. The average rate of advance was 7.5 m per day with a maximum of 12 m/day. The last years of the 1900s saw the arrival of what came to be known as “computerized drill rigs.” These are also known as CAN-bus rigs because they are equipped with a control system that is completely digitalized. The word CAN stands for Controlled Area Network and means that all commands are transmitted with a digital code via a cable loop to which a variety of functions are connected. For example, when a command is transmitted from a centrally located computer on the rig to a hydraulic valve, the command includes an address

ATLAS COPCO UNDERGROUND CONSTRUCTION – TALKING TECHNICALLY

TUNNEL EXCAVATION: A LOOK BACK IN HISTORY

and a task. So how do these technical achievements described above affect the tunneling performance? Looking back over more than 100 years, we can conclude that a driller today can achieve 100 times more than a driller who worked on the first tunnel at Fréjus. It is also somewhat surprising to note that the first Fréjus tunnel was completed in 13 years while the second tunnel took five years to complete. This means that in 100 years, the speed of tunneling has only increased by 2.5 times. When comparing this to developments in other areas of technology, we can conclude that we travel at least 5–10 times faster on rails these days than we did a hundred years ago. Does this mean that technological developments in drilling technology have contributed so little to the end result? The answer is “no” for although today’s construction projects take 50% to 25% of the time they did 100 years ago, the size of today’s workforces is considerably less. On the first Fréjus tunnel, more than 4 000 people were required to get the job done, while the second Fréjus tunnel needed a workforce of less than 400. As a consequence of technical developments, the working environment and safety aspects have drastically improved.

Development of rock support

Rock support goes hand in hand with rock excavation. The development of the technique and the materials used have had a large impact on the growing trend to locate different facilities underground rather than on the surface. Effective ground support has made it possible to build economically even in poor ground conditions. Going back some 200 years or more to the few, short tunnels that were constructed, we can see that the ground was mainly self-supporting, meaning that there was no need for rock support. This meant that tunnel profiles sometimes deviated from their intended shape. The use of brick lining as a permanent support arrived in the early to mid-1800s when tunnel excavation was for civil purposes instead of just being temporary accesses to mines. The linings consisted of ordinary bricks with filling material behind the brick arch, creating contact between the rock wall and roof and the load bearing arch. This type of rock support was installed close to the face or after the excavation had been completed, in which case temporary support was needed to stabilize the ground as the excavation proceeded. Up to the early, mid-1900s, this was standard practice in many parts of the world when tunneling took place in unstable conditions. Judging from the thickness of the lining and the invert strutting, it is obvious that heavy pressure from overlying rock was expected.

crete-based lining soon became the norm in tunnel construction. Concrete spraying and bolting were known methods in the early 20th century but not extensively used. The dry mix type of sprayed concrete became more widely used in the 1950s. The nozzle action was entirely manual, and the operator held it with both hands. Already in the early 1960s, rigs for maneuvering the nozzle were introduced, and with that the old brick linings for permanent support became completely obsolete. When tunneling in strong crystalline basement rock, insitu concrete linings were only rarely used. In those cases, sprayed concrete was used both as primary and secondary linings. The sprayed concrete was mostly applied in connection with the installation of rock bolts. Bolts had been used in mining and were now well accepted in the civil construction industry, both the pre-stressed type as well as the dowel type. Knowledge of the interaction between the support and the rock itself came with the works of Therzagi in the 1930s, during which the timing factor for the installation of support was introduced. The science of rock mechanics was introduced after the Second World War by a group of researchers in Salzburg, Austria, in which Leopold Müller played a major role. This group started the geo-mechanic colloquium, a seminar on rock mechanical issues in relation to surface and underground construction. They held their annual meetings in Salzburg, and these meetings are still held there today. It was in this environment that the well-known “New Austrian Tunneling Method” NATM was created. It is easy to understand that this approach to tunnel excavation and rock support was embraced by many when studying the concept of the traditional Austrian tunneling method. However, it

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Tunneling overview

Up to the mid or early 1900s, temporary support elements were mainly constructed in wood. In the 1930s, steel was being used extensively as primary support because steel arches became available at an acceptable cost. A final con-

The Atlas Copco Boomer was introduced in the 1970s and became a standard rig for tunneling and drifting, marking the entry of hydraulic drilling equipment.

TUNNEL EXCAVATION: A LOOK BACK IN HISTORY

must be said that this technique has been misinterpreted by many tunnel builders who believe that they are applying this technology as soon as they use sprayed concrete support. The whole concept of “ground reaction” in relation to tunnel excavation and support has paved the way for tunneling in poor ground conditions, especially when there is large overburden. Up until the present day, NATM technology is frequently applied in tunnel support, although there is a tendency to avoid intense splitting of the tunnel face and to carry out the excavation in stages. This is one way to control the deformation. The splitting work is time-consuming, and an alternative to improve the stability of the ground ahead of the face, and thus reduce or eliminate the splitting, has become more widely used. Consequently, pipe roofing and spiling currently play a major role in poor ground excavations. Support of the tunnel face itself by bolts in the form of long fiber strands are only applied where major deformations of the face are foreseen. Secondary linings today consist of either concrete or sprayed concrete. The choice depends on the geology but is also influenced to a large extent by the conventional design of having a final lining that is capable of handling the entire rock load, not including the primary support as a part of the final lining. In Scandinavia, which has mainly competent crystalline basement rock, sprayed concrete lining is the dominant method, but in similar rock conditions in Hong Kong and, to a large extent, in India, concrete lining is the preferred method. In regions dominated by sedimentary rock, concrete lining is by far the preferred method, even when tunnels are excavated in igneous rock. Segmental lining as a single shell method of support is commonly used in connection with TBM (Tunnel Boring Machines) tunnel excavations. It was introduced in the 1960s but became widespread in the 1970s, particularly in soft ground tunneling. The Japanese developed the slurry technology that suited the fast growing city of Tokyo, which is founded on thick layers of mainly friction soils. The advent of TBM tunneling meant that the extensive cut-and-cover tunneling used at that time could be abandoned, much to the relief of the citizens.

Mechanical excavation

Tunneling by use of mechanical excavation instead of by means of blasting agents started in the 1950s, albeit on a very small scale. It was the mining engineer James Robbins who built the first TBMs where the so-called disccutter was the cutting tool. More than 100 years earlier, TBM excavations had been made under the river Thames in London, but during that project only ripping teeth were used to cut through the London clay. The first generation of TBMs had relatively small disc cutters capable of

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dealing with loads of about 8 tonnes, while the TBMs of today can handle loads of up to 35 tonnes. Certainly the cutters have grown in size and so has the rock surface on which the cutter is pressing. The net result is that the penetration of the cutters has drastically improved, especially in very high strength rock formations (300 MPa) where the TBMs with small cutters had penetration in the range of fractions of a millimeter, while today, in similar conditions, they are in the range of 4 mm per cutter-path or full 360 degree rotation of the cutter-wheel. However, most TBM tunneling is made in sedimentary rock, which is not surprising considering 70% of the Earth’s land mass is covered with sedimentary rock. The lower strength of the sedimentary rock material allows for good penetration, and consequently many tunnel meters can be achieved per day. Over the years, the TBMs have become more powerful as cutters have become more capable of taking on even larger loads. This means that the TBM technique is doing more of the tunneling that was previously done by the drill and blast method. The TBM technique has also increased the amount of tunnel meters being driven worldwide as decision-makers have become increasingly aware that this solution is economically viable for many new applications, such as tunnels instead of bridges and trenches. As a result it is clear that the total number of tunnel meters created by drill and blast has most likely not been reduced by the introduction of the TBM. Over the past 15 years, cutting technology has not been developed very much, aside from an increase in cutter sizes and applied cutting power. However, transporting the broken rock (muck) via conveyors has become very common. Conveyor mucking offers a continuous process with a high capacity. The soft ground TBM technique has certainly been embraced by city planners and decision-makers when it comes to tunneling for subway systems. The capability of dealing with a great variety of soil conditions at moderate depth is a big success story. A large number of TBMs are presently at work upgrading the transportation systems for some major Chinese cities. Roadheader excavation of tunnels entered the construction market in the 1960s. This machine has its origin in the mining industry, primarily in coal mining. They became fairly popular in the 1970s and 1980s when they were used to excavate tunnels in sedimentary rocks and soft materials. But as the TBMs became more competitive in this type of ground, even for shorter tunnels, the demand for roadheaders diminished. The drawback of roadheader technology is its strong dependence on the strength of the excavated rock material. For small tunnels, this was more obvious as the smaller machines are very limited in terms of rock strength, and all machines, whatever their size, have problems if the rock is very hard and abrasive. Today, there is very little left of roadheader tunneling in civil construction. ◙

ATLAS COPCO UNDERGROUND CONSTRUCTION – TALKING TECHNICALLY

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Tunneling overview

Workers from the French and Italian side of the Alps meet at the middle of the Mont Blanc Tunnel, completed in 1965.

Global outlook: Continued population growth and urban expansion around the world will require new tunneling projects and upgrades to existing infrastructures.

The essential role of tunnels: a look into the future

Creating a functioning yet sustainable society is one of the great issues of the 21st century. Fortunately, man’s ability to construct tunnels goes a long way to solving an array of challenges in the most efficient way, from transportation to water supply. The tunneling industry is entering its most rapidly evolving and, arguably, most exciting era. Whether in good economic times or bad, tunnels are an essential component of functioning societies all around the world. They are indispensable for public transport, roads and rail networks, for supplying fresh water to cities, building sewage systems, constructing hydropower stations that generate renewable energy, and providing facilities for storage, communications and a range of other applications. In the future, underground construction will undoubtedly increase to meet the growth of urban populations and the

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continued expansion of infrastructure in and between cities. Furthermore, existing tunnels must also be upgraded so that modern standards for safety and efficiency are upheld and guaranteed for the 21st century. So, what are the most important trends from a global perspective? They can be revealed by studying the key factors that characterize the tunneling industry of today: volume of rock, excavation methods used, safety aspects, costs, the availability of labor, type of underground openings, and geology.

ATLAS COPCO UNDERGROUND CONSTRUCTION – TALKING TECHNICALLY

THE ROLE OF TUNNELS: GLOBAL MARKET OVERVIEW

Tunnel Construction output by geographical areas Europe North America Japan China India South America Others 0

20 000

40 000

60 000

80 000

100 000

Figure 1: Annual construction costs in million USD. (Source: ITA-AITES, International Tunnelling and Underground Space Association).

The global picture: excavation volumes

In contrast to the mining industry where volumes are measured in tonnes, excavation volumes in tunnel construction are exclusively described using solid cubic meters (m3) as a reference. A typical exception to this rule is the haulage capacity of conveyor belts and trucks where the concept of tonnes may also be used in addition to cubic meters (m3). Although annual excavation volumes from underground construction grow over time, they are not constant and fluctuate. The reason is that tunneling projects are very large and complex undertakings, fraught with challenges that need to be overcome, and this may affect growth statistics. While it is very difficult to provide exact figures, the generally accepted view is that the total annual volume from underground excavations in rock is somewhere in the range of 100 million m3. According estimations by ITA-AITES (International Tunnelling and Underground Space Association), the total volume including soft material will be almost double.

As the combined populations of India and China have already surpassed 2.5 billion, it is more than reasonable to assume that many new subway lines will be needed to meet the demand for increased public transportation capacity as more and more people choose to relocate to cities. It has also been estimated by ITA that the value of the annual global underground construction is in the region of USD 90 billion which corresponds to roughly 5 000 km of tunnels. How this dollar value estimation is divided across the world’s regions is illustrated in Figure 1.

Growth in Asia

China is currently the nation with the largest underground construction schemes, where some 40 million m 3 of rock

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Tunneling overview

The figure, which is only a fraction of annual volumes in mining, can be visualized and more easily referenced by imagining a cube of rock that has a side length of 470 m. An easier way, perhaps, of relating to this figure is to convert it into kilometers of subway tunnel. In a typical scenario where

a single-track tunnel has a cross section of 30 m2 with added volumes for stations at every 1 to 1.5 km, the figure 100 million m3 will correspond to 3 000 km of single-track subway. For the sake of useful comparison, one might consider the city of Stockholm, the Swedish capital, as an example as it has roughly 1 million inhabitants and a 100 km long doubletrack subway system. The global annual figure for excavation volumes in tunneling would be the equivalent of developing new subway systems in 15 Stockholm-sized cities.

THE ROLE OF TUNNELS: GLOBAL MARKET OVERVIEW

km

Total length of metro lines in operation in China

1 700

1 699

1 600

1 471

1 400 1 200 999

1 000 763

800 600

835

621

400 200 0 2006

2007

2008

2009

2010

2011

Figure 2: Increase of subway line construction in China in kilometers over recent years. (Source ITA-AITES, International Tunnelling and Underground Space Association).

are excavated. This corresponds to 40% of the world’s total underground construction operations in rock. In this approximate figure, 500 km of road and railway tunnels will most likely represent 30 million m3. The rest is comprised of excavations for hydropower facilities and a program for storing hydrocarbons in unlined rock caverns. To be able to maintain its policy of storing three months of the national consumption of oil, China will require a storage capacity of 60 million m3. The current designated program stipulates that construction over a 10-year period will result in 6 million m3 annually of excavated volume. A large share of the oil reserves will, however, be stored in steel tanks.

where there is significant potential for hydropower. These projects in Bhutan are often financed by Indian capital, and most of the designs require long and large tunnels with underground power stations, meaning that the excavation volumes will be large. Major cities in India, such as New Delhi, Kolkata (Calcutta), Bangalore and many others, are already building new railway transport systems. A large proportion of these are being developed underground.

The annual figure for underground excavation in soft material exceeds the rock excavation volume. More than half of the worldwide underground volumes (estimated at about 200 million m3) is excavated in China. An example of this growth is demonstrated in Figure 2, showing where subway lines have been extended by more than 1000 km over a five-year period.

Just like its neighboring country China, India also has a program for storing hydrocarbons in unlined rock caverns. Although the program is a lot smaller, it still contributes millions of excavated cubic meters. Indochina (Myanmar, Cambodia, Laos, Singapore, Thailand and Vietnam) also has a strong potential for hydropower, particularly in Vietnam and Laos. Here, construction is moving forward continuously as more and more end-customers in Vietnam and Thailand are prepared to accept the price of electric energy.

The remaining regions of Asia represent some 25% of the global underground excavation volumes. Here we see hydropower construction increasing its volumes, not just along the rivers that dewater the Himalayas in India, but also in Bhutan

Moving on to Japan, which comes second place after China in terms of excavated volumes despite declining figures in recent years, road tunnels make up the largest share of underground construction volume followed by railway tunnels.

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THE ROLE OF TUNNELS: GLOBAL MARKET OVERVIEW

European outlook

Europe is the third largest market for underground construction with an annual volume that amounts to 13 million m3 of rock, which corresponds to 15% of worldwide volumes. Among the projects, road and railway tunnels are the dominating structures. Hydropower accounts for a small share of the total volume as most locations that are suitable for hydropower generation have already been developed, and power stations have been installed. Nonetheless, there is a continued market for hydropower construction in Europe because many facilities will need to be modernized in the years ahead. Very few hydropower stations are older than 100 years, yet numerous facilities are in dire need of upgrading basic structures, such as tunnels, waterways and caverns. Pump storage schemes are necessary supplements to electricity generated from wind power, which is also likely to see growing interest in the coming decades. At the same time, excavated volumes of rock and soil for these structures are quite small by comparison and have a negligible impact as far as statistics are concerned. Major tunnel projects are in the planning stages, including rail and subway projects, that will contribute large volumes of excavated material to these statistics. Out of the total world output of USD 90 billion annually, Europe represents more than 10% and will, most likely, continue to do so. An Atlas Copco Boomer E2 C drill rig is hoisted via cable car installations to the Project Linthal 2015, a hydropower construction site in the Swiss Alps.

Modernization in the North America

Underground construction in the U.S. is mainly focused on tunnels for roads and subway lines, although a considerable share also deals with stormwater storages and sewage systems. The excavated volumes of rock are just over half of those recorded in Europe, and the numbers for soft ground excavation are far lower than the European ones. As is true in Europe, where infrastructure roughly meets current demand, much of the tunneling being done involves the upgrade and replacement of old underground structures. These are designed to meet the gradually increasing demand for capacity as the populations of the larger cities increase. The major underground works taking place in New York City to expand and upgrade the public transport system are a good example (see case article on p. 242).

South America on the rise

In South America, some nations are still in the development phase, and there is a growing need for both infrastructure and power. Furthermore, the continent has great potential for generating hydropower that may be beneficial in meeting the increased demand for energy.

Other regions

For Africa and Australia, the underground volumes in construction are small when compared to the other continents, and they are estimated to be below or in the range of 1% of the total figure. Having said this, a number of countries in Africa are developing rapidly, and the demand for energy is undoubtedly destined to increase immensely. With many suitable locations for renewable hydropower, particularly in central parts of the continent, tunnels will also be required. It remains to be seen to what extent these facilities will involve underground structures.

Excavation methods

From the perspective of giving a global insight into the tunneling industry and where it is headed, the type of excavation methods used is another important aspect. There are currently three methods that dominate practices worldwide – drill and

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Tunneling overview

In the Andes mountain range, many tunneling projects will be required if roads and railways are to be built according to modern standards for high speed. Underground construction

in rock corresponds to roughly half of the European volumes, about 6 million m3 per year. Large railway projects are underway in Brazil, indicating that excavation volumes will increase in the near future.

THE ROLE OF TUNNELS: GLOBAL MARKET OVERVIEW

Excavation methods

100% 90% 80% 70% 60% 50% 40% 30% 20%

Other methods

10%

TBM Drill and Blast

0% Austria

India

USA

Chile

Japan

Figure 3: Tunneling is dominated by two main excavation methods; TBM (Tunnel Boring Machine) and drill and blast. The choice is largely dictated by geology and the tunnel design. Soft rock (TBM) is more prevalent in North America while hard rock conditions characterize European tunneling (drill and blast).

blast excavation, mechanical excavation by use of Tunnel Boring Machines (TBMs) and mechanical excavation using road headers. As shown in Figure 3, the distribution of excavation methods in rock, hard to loose, varies greatly between different regions, but also over time as technologies develop. A large share of TBM excavations are carried out in soft ground conditions, and this is also the most common method for developing subway tunnels in large cities. It is also used to some extent for road and rail tunnels. Many of today’s metropolitan areas were founded as cities centuries back when shipping was the principal method for transporting goods. This means that large cities are often located along river estuaries because they conveniently linked the sea with the inland, thereby linking consumers and traders with producers. What is more, river outlets are generally considered major settlement areas for sediments brought in by the rivers. Typical examples of this are Shanghai, Tokyo, and Amsterdam. By contrast, cities such as Hong Kong, Stockholm, and Sydney have opposite conditions where most buildings are founded on solid rock or have a short underpinning down to the solid rock.

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As a consequence of the above, it is estimated that about two-thirds of all TBM excavation work is carried out in soft ground conditions. A typical nation that favors TBM is the U.S. where more than 90% of tunnels are driven by TBM. A typical non-TBM nation is Finland, which to this date has not had a single TBM project as all excavations have been performed by drill and blast. Japan is a nation where rock excavation projects tend to favor drill and blast. A reason for this is that a major share of the market consists of large tunnels of moderate lengths for road networks, conditions for which this method is wellsuited. There are a number of aspects influencing this large discrepancy between countries and the types of excavation methods used. Geology is one important factor. It is well-known that high strength rock (UCS 200 MPa) does not favor the use of mechanical excavation. While practically possible, it is, in most cases, simply not economically viable. By contrast, sedimentary rock with a low quartz content does favor mechanical excavation, as tunneling in soil using the drill and blast method is less than ideal.

ATLAS COPCO UNDERGROUND CONSTRUCTION – TALKING TECHNICALLY

THE ROLE OF TUNNELS: GLOBAL MARKET OVERVIEW

Recruiting skilled professionals

The availability of skilled staff is a crucial issue for the tunneling industry as a whole. One reason for this is that fewer and fewer personnel have enough experience with conventional excavation methods. The drill and blast method offers a certain flexibility when facing varying ground conditions that is not possible to achieve with TBM equipment. But there are other reasons, too. Flexibility is key for today’s contractors, and that puts greater demands on finding personnel who are willing to travel and work in different countries, often in strenuous conditions. In the U.S., a result of this development is that drill and blast is now only employed to a marginal degree as it has proven to be easier to train people for operating and handling a TBM excavation. Although geology and the availability of personnel have proven decisive in terms of tunneling methods, there are other important factors that have more to do with tradition and the type of tunnels that are in demand. A good example of this is Japan, which has many drill and blast projects despite the fact that the country is largely characterized by soft ground conditions. Japan has developed a large number of road tunnels with large cross sections in areas that are not dominated by soft ground. In the 1980s, the situation was very different because projects tended to be located in the typical soft ground areas. Austria is another country where drill and blast excavation has traditionally been the method of choice. However, Austrian contractors are now increasingly embracing mechanical excavation methods as their Swiss neighbors have been doing for the past few decades.

Safety comes first

In addition to the above, the choice of tunneling method is, to a large extent, dictated by economic factors. Achieving the lowest possible costs for a project is always a strong incentive for choosing one method over another, but safety and risk assessments must always come first. The hydropower facilities that are being excavated in the Himalayan mountains in India, where rock mechanical conditions are highly challenging, are a good example of how estimated risks have been decisive in choosing between a drill and blast or TBM excavation process. In this case, a number of TBM projects did not turn out as expected which has brought about a more realistic view on which conditions the excavation methods can handle.

In addition to the risk factors associated with tunneling projects, speed of excavation and costs are key factors to consider,

and they will always vary depending on the location of the project, the availability of skilled labor, salaries, regulations, and more. Comparing the excavation rate between one method and another is relatively easy to do when ground conditions are known beforehand. This is, unfortunately, not the case for the vast majority of tunneling projects, which means that completion dates and costs are usually quite difficult to establish. This fact becomes obvious when comparing the accuracy of estimations for structures such as houses and bridges where almost all work is carried using well-defined materials. At the Lötschberg tunnel in Switzerland, one of two Alp transit tunnels excavated in the most recent decade, a section of the excavation offered the opportunity to make a comparison in practice. Over a parallel tunnel excavation, one tunnel was excavated by TBM and the other by drill and blast. As the result shows in Figure 4 (next page), the average advance rate for the drill and blast method is roughly half that of the TBM method, although there are deviations depending on which tunnel is considered. A cost comparison has also been made. Here, it can be concluded that the TBM excavation has been completed at a lower cost in poorer ground conditions and vice versa in better ground conditions, in reference to rock stability.

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Tunneling overview

Cost and excavation rate

Finland is a typical non-TBM nation . All tunnel excavations to date have been performed with the drill and blast method.

THE ROLE OF TUNNELS: GLOBAL MARKET OVERVIEW

35

meters/day

Advance rates at the Lötschberg tunnel in Switzerland

30 25 20 15

TBM maximum

10

TBM average

5

D&B maximum

0

D&B average PA 11

PA 12

PA 14

PA 15

PA 16

PA 18

Figure 4: Average and maximum advance rates for the tunnel reach during the Lötschberg Base Tunnel excavation, Switzerland.

This is not unusual as long as the ground conditions are moderately poor. In very poor ground, there are numerous cases where a TBM has got stuck, and the excavation has been abandoned in favor of drill and blast excavation. This means that a successful TBM excavation is heavily dependent on pre-investigations regarding the geology along the tunnel route, which, therefore, are normally more extensive. It is a prerequisite that all parties involved can contribute to ensuring that the time schedule and costs are as accurate as possible.

Innovation leads the way

As cities expand around the world to cater to growing populations, tunnel designs are getting more complex. A common effort to meet this challenge is perhaps the biggest industry trend at the present time. It goes hand-in-hand with safety, the need for expertise, ground conditions and costs. Innovation is driving the industry forward, and new technologies are

24

becoming increasingly available. The use of sprayed concrete to stabilize tunnels as they are driven has revolutionized the tunneling industry in just a few years. The use of 3D technologies and advanced data management software are also becoming widespread. These technologies have also paved the way for far greater precision in the excavation process, which governs both time and costs. But that’s not all. The conditions for financing tunneling projects are also changing rapidly, and the importance of environmental concerns will only grow in the years ahead. In fact, there are many indications that the demand for tunnels will increase significantly as the lack of space and environmentally acceptable solutions on the surface of the planet become more evident. All of these issues and more will be looked at more closely in the following chapters of this technical reference book for tunneling practices. ◙

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Tunneling overview

ATLAS COPCO UNDERGROUND CONSTRUCTION – TALKING TECHNICALLY

1 2 3 4

1000

2000

3000

4000

5000

(km)

6000

1 Earth Crust 2 Mantle 3 Outer Core 4 Inner Core

Figure 1: The Earth’s interior consists of four main layers. Heavy metals such as iron and nickel are most abundant in the core. 1 2 3 4

Earth Crust Mantle Outer Core Inner Core

Tackling the challenges of sub-surface space A deep understanding of geology and of the nature and characteristics of the rock and soil at a proposed tunnel site, are prerequisites for successful tunnel excavations. Selecting the method, choosing equipment, designing a rock support system and a dozen other key decisions that will affect the success of a tunnel construction project, are all directly related to geology and rock characteristics in and around a proposed tunnel site. Conversely, without a thorough knowledge of the geological facts, these decisions could have potentially disastrous consequences. Although geologists have not probed the planet to its core, they are confident in their grasp of what the Earth looks like beneath its crust, and of the properties of the various rock

26

types that have been formed over millions of years. What is important to the tunneling engineer, however, is how this expertise impacts on the practical realities of tunnel construction.

How the Earth was made

The Earth consists of an inner and an outer core surrounded by a mantle. At the surface is a thin layer of rocks known as the crust, shown in Figure 1. This shell-like structure has been confirmed by studying seismic waves originating from

ATLAS COPCO UNDERGROUND CONSTRUCTION – TALKING TECHNICALLY

GEOLOGY AND WHY IT MATTERS

Samples of common rock types: Amphibolite, Diabase, Dolomitic limestone, Gneiss, Granite, Sandstone.

earthquakes. The velocity, or propagation, of these waves is related to the density of the material and its state, be it solid or liquid. According to this interpretation, the inner core is solid and the outer core is liquid. The mantle and the thin crust of the Earth are solid, apart from the shallow layer of the mantle, also known as the “upper mantle”, which is composed of plastic flowing rock about 200 km thick. The motion of this layer forms the basis of plate tectonics. The thickness of the core and mantle each correspond to roughly half of Earth’s radius and we can observe only the upper part of the Earth’s crust. The deepest drill hole is 11 km, but we can get information from the equivalent of tens of kilometers by studying eroded mountain chains. Earth was formed more than 4.6 billion years ago by aggregation of cosmic material from our solar system. The meteorites falling down on Earth are of the same origin as our planet so, by studying this material, we can get data about the chemical composition of the deeper sections of the core.

However, there is a great difference in thickness between oceanic crust and continental crust. Under a mountain chain the crust thickness can be up to 70 km. The chemical composition of the outer part of the crust is well known, and is dominated by eight elements: oxygen, silicon, aluminum, iron, magnesium, calcium, sodium and potassium. The continental crust is higher in silica, aluminum and alkali due to the high content of granitic rocks. The oceanic crust is lower in silica but higher in magnesium and iron due to the dominance of volcanic rocks, mainly basalts. Of the 155 known elements, some of which do not occur naturally, oxygen is by far the most common, making up about 50% of the Earth’s crust by weight. Silicon forms about 25%, while aluminum, iron, calcium, sodium, potassium, magnesium, titanium, silicone, oxygen and other common elements build up the total to 99% of the Earth’s crust. Silicon, aluminum and oxygen occur in the most common minerals

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Rock classification

There are two types of meteorites: stone meteorites dominated by Fe-Mg-silicates, or chondrites; and iron meteorites mainly consisting of metallic iron and nickel. Seismic and meteorite data indicate that the chemical composition of the core is

similar to iron meteorites and that of the mantle is similar to stone meteorites. The difference in density also explains the velocity of seismic waves in the core and mantle, and the high average density of the earth, which is about 5.5 g/cm3. The thickness of the crust is normally between 10 and 35 km.

GEOLOGY AND WHY IT MATTERS

1

9

2

10

11

3

12 13

4 5

14

6

15

7 8

1 North American plate 2 Juan de Fuca plate 3 Caribbean plate 4 Cocos plate 5 South Amercian plate

6 Nazca plate 7 Scotia plate 8 Antarctic plate 9 Eurasian plate 10 Pacific plate

11 Arabian plate 12 Indian plate 13 Philippine sea plate 14 African plate 15 Australian plate

Figure 2: The tectonic plates were mapped in the second half of the 20  th century. They consist of the Earth's crust and uppermost mantle, together referred to as the lithosphere.

such as quartz, feldspar and mica, which form part of a large group known as silicates, being compounds of silicon and other elements. Amphiboles and pyroxenes contain aluminum, potassium and iron. Some of the planet’s most common rocks, granite and gneiss, are composed of silicates. Oxygen also occurs commonly in combination with metallic elements which are often important sources for mining purposes.

which includes the whole of South America and a part of the Atlantic, and the African plate consisting of the African continent and parts of the Atlantic and Indian Oceans.

Plates can interact by moving apart (divergence) or towards each other (convergence). When two continental plates collide, mountain ranges may be formed (see Figure 3). Thus the collision of the Indo-Australian and Eurasian plates resulted in the formation of the Himalayas, the highest mountain chain 1 North American plate 9 Eurasian plate Tectonic plates on earth. When an oceanic plate moves towards a continental 2 Juan de Fuca plate 10 Pacific plate The modern3theory of plate tectonics has improved our underplate such as South America, the oceanic plate will move Caribbean plate 11 Arabian plate standing of 4basic geological processes like formation of rock Cocos plate 12 Indian platebelow the continent, or subduct. When the oceanic plate starts volcanism, 5earthquakes and theplate formation of many of sea to melt, South Amercian 13types Philippine plate volcanic activity will occur. Therefore, we find a 6 Nazca plate 14 African plate ores. great number of volcanoes along the western part of South 7 Scotia plate 15 Australian plate America, to mention one example. Subduction also leads to plate According 8to Antarctic this theory, the crust and upper part of the the formation of ores. mantle can be divided into 10 to 12 major plates, which move in a complex pattern (see Figure 2). The driving force of this In the middle of the Atlantic there is a long chain of volcamovement can be attributed to heat generated by radioactive noes called the mid-Atlantic ridge. Similar ridges are found decay within the mantle and core. The heat is transported by in the other oceans. Along these ridges two oceanic plates slow convection streams, which move the plates and the speed are moving apart as magma rises from the mantle below and of the motion of plates is just a few centimeters per year. solidifies. This causes repeated eruptions of basaltic lava, forming a new ocean floor. The youngest volcanic rocks Three major plates are North American which includes are found close to the ocean ridge, and the age of the rocks North America, Mexico and Greenland, South American increases out from the spreading center. The mechanism of

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ATLAS COPCO UNDERGROUND CONSTRUCTION – TALKING TECHNICALLY

GEOLOGY AND WHY IT MATTERS

3 2

1

1 Collision zone 2 Oceanic ridge, spreading zone 3 Subduction zone

Figure 3: Tectonic plates interact by moving apart (divergence) or towards each other (convergence). When an oceanic plate moves toward a continental plate, the oceanic plate moves below the continent which creates a subduction zone.

seafloor spreading is an important part of the plate tectonic theory. Volcanic activity occurs above hotspots and in spreading zones. There are three types of volcanoes that are shaped by their tectonic surroundings: rift volcanoes, emerging in spreading zones: stratovolcanoes, which are located along the subduction zones: and shield volcanoes, located above hotspots. Volcanism also occurs due to the collision of plates but is distinguished from earthquakes, as these occur when two plates are sheared or slide along each other, such as in Los Angeles, and not from the movement of magma.

mixed, consisting of both homogenous and heterogeneous structures. In addition, minerals have a wide variety of properties and characteristics, including the following: • Hardness • Density • Color • Streak • Luster • Fracture • Cleavage • Crystal structure

Mineral properties and characteristics

The particle size and the extent to which the mineral is hydrated (mixed with water), indicate the way the rock will behave when excavated. Hardness is commonly graded according to the Mohs 10-point scale, as shown in Table 2. The density of light colored minerals is usually below 3 g/cm3. Exceptions are barite or heavy spar (barium sulphate – BaSO4 – density 4.5 g/cm3), scheelite (calcium tungstate – CaWO4 – density 6.0 g/cm 3) and cerussite (lead carbonate – PbCO4 – density 6.5 g/cm 3). Dark colored minerals with some iron and silicate have densities of between 3 and 4 g/cm 3. Metallic ore minerals have densities over 4 g/cm3, and gold has a very high density

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Rock classification

A mineral is a natural chemical compound with a defined crystal structure and composition. A rock, on the other hand, is a naturally formed aggregate of minerals. There are thousands of different minerals but only about fifty rock-forming ones, most of which are silicates, always containing silicon and oxygen. Feldspars account for almost 50% of the Earth’s crust and are hence the most common mineral (see Table 1). Feldspars can be grouped in alkali feldspar and plagioclase. The second most common minerals in the crust are pyroxene and amphibole followed by quartz and mica. Together these minerals make up about 90% of the Earth’s crust. It is true to say that mineralization is rarely pure. Instead, it is usually

n tio za lli a t ys

MAGMA

Sm el tin g

Me tam orphis m

RY

g erin p. Weath trans Erosion

PHIC MOR TA S ME ROCK

MA GM RO ATIC CK S

C r

GEOLOGY AND WHY IT MATTERS

SE

D

IM

TA EN S M K DI OC E R S

EN TS

Cementation

Figure 4: The rock forming cycle shows the creation of various rock types and how they deteriorate.

Rock forming minerals Feldspar

58%

Pyroxene and amphibole

13%

Quartz

11%

Mica

10%

Olivine

3%

Others

5%

Table 1: Feldspar is the most common rock forming mineral.

Hardness grading Moh´s hardness scale

Typical mineral

Identification of hardness

1

Talc

Easily scratched with fingernail

2

Gypsum

Barely scratched with fingernail

3

Calcite

Very easily scratched with a knife

4

Fluorite

Easily scratched with a knife

5

Apatite

Can be scratched with a knife

6

Orthoclase

Difficult to scratch with a knife, but can be scratched with quartz

7

Quartz

Scratches glass and can be scratched with a hardened steel file

8

Topaz

Scratches glass and can be scratched with emery board /paper (carbide)

9

Corundum

Scratches glass. Can be scratched with a diamond

10

Diamond

Scratches glass and can only be marked by itself

Table 2: Hardness is commonly graded according to the Moh's 10-point scale.

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of 19.3 g/cm 3. Although ore forming mineral density may be high, the total ore density depends entirely on the host rock where these minerals exist. Streak is the color of the mineral powder produced when a mineral is scratched or rubbed against unglazed white porcelain, and may be different from the color of the mineral mass. Fracture is the surface characteristic produced by breaking a piece of the mineral and is usually uneven in one direction or another. Cleavage denotes the properties of a crystal whereby it allows itself to be split along flat surfaces. Both fracture and cleavage can be important to the structure of rocks containing substantial amounts of the minerals concerned. Rock normally comprising a mixture of minerals, not only combine the properties of these minerals but also exhibit properties resulting from the way in which the rocks have been formed, or perhaps subsequently altered by heat, pressure and other forces in the Earth’s crust. The mineral composition of rock is key to our understanding of the behavior of rock and how natural stress fields and fracture properties come into play. Stress fields in the rock arise partly because of the rock mass weight, but also due to movements caused by geological processes. Rock mass is a synonym of bedrock and refers to the rock plus discontinuities in the rock amassed in large volume. These discontinuities are important not only for the structural integrity of a tunnel, but also as paths for fluids in the Earth which cause mineral concentrations.

Appraising the rock

For drilling during tunnel construction, the rock must be correctly appraised as the results will affect projected drill penetration rates, hole quality and drill steel costs. In order to determine overall rock characteristics, it is necessary to distinguish between microscopic and macroscopic properties. As rock is composed of grains of various minerals, the microscopic properties include: • Mineral composition • Grain size • The form and distribution of the grain • If the grains are loose or cemented together Collectively, these factors comprise the properties of the rock, such as hardness, abrasiveness, compressive strength and density. In turn, these rock properties determine the penetration rate that can be achieved when drilling blastholes and the extent of the wear on the drilling equipment. In some circumstances, certain mineral characteristics will directly influence the tunneling method. Many salts, for example, are especially elastic and can absorb the shock from blasting.

Rock drillability

Drillability depends on the hardness and brittleness of the rock’s constituent minerals and on the grain size and crystal habit, if any. For example, quartz, which is one of the

ATLAS COPCO UNDERGROUND CONSTRUCTION – TALKING TECHNICALLY

GEOLOGY AND WHY IT MATTERS

Typical igneous (magmatic) rock types Silica (Si02) content

Intrusive (plutonic rocks)

Hypabyssal (dykes and sills) Extrusive (volcanic)

Ultramafic 63% SiO2

Granodiorite

Granodiorite porphyry

Rhyodacite

Granite

Pegmatite

Rhyolite

Table 3: Main igneous rock types according to chemical composition (silica content) and location where magma turned into solid rock.

commonest minerals in rock, is a very hard material, exceedingly hard to drill and will certainly cause heavy wear, particularly on drill bits. This is known as abrasion. Conversely, a rock with a high content of calcite can be comparatively easy to drill and cause little wears on drill bits. With regard to crystal habit, minerals with high symmetry, such as cubic galena, are easier to drill than those with low symmetry, such as amphiboles and pyroxenes. In terms of drillability, rocks with essentially the same mineral content may be very different. For example, quartzite can be fine grained (0.5-1.0 mm) or dense (grain size 0.05 mm). A granite may be coarse grained (size >5 mm), medium grained (1-5 mm) or fine grained (0.5-1.0 mm). A rock can also be classified in terms of its structure. If the mineral grains are mixed in a homogeneous mass, the rock is termed massive (isotropic), as with most granite. In mixed rocks, the grains tend to be segregated in layers (anisotropic), whether due to sedimentary formation or metamorphic action from heat and/ or pressure.

Rock formations

There is a relationship between magmatic, sedimentary and metamorphic rocks, as shown in Figure 4. Starting with the magma at the top of the figure and going down to the left, the magma will crystallize into a magmatic rock due to decreasing temperature and pressure. If crystallization occurs within the crust, an intrusive rock results, for example, granite. If the magma is erupted by volcanic activity, the result will be rhyolitic lava, or a tuff of similar composition. All rock formations irrespective how they were formed exposed to surface conditions are being weathered and eroded by both chemical and mechanical processes. Chemical weathering will decompose many minerals, but the remaining part of more resistant minerals and rock fragments will be transported by water, ice or wind until deposition occurs.

However, there are also some other possibilities. When metamorphic rocks are exposed at the earth’s surface, weathering starts and the cycle is short-circuited. Erosion and weathering will transform the rock into sediment, which later can form a sedimentary rock. There is also a possibility that a magmatic rock is metamorphosed without forming a sedimentary rock in between. In other words, recycling of rocks is a constant, ongoing process. It is therefore important to identify the rock’s origins which are divided into three classes: • Igneous or magmatic – formed from solidified lava at or near the surface, or magma underground • Sedimentary – formed by the deposition of reduced mate rial from other rocks and organic remains or by chemical precipitation from salts, or similar • Metamorphic – formed by the transformation of igneous or sedimentary rocks, in most cases by an increase in pressure and heat.

Igneous or magmatic rock

Igneous rocks are formed when magma solidifies, whether plutonic rock, formed deep in the Earth’s crust as it rises to the surface in dykes cutting across other rock or sills following bedding planes, or volcanic, as lava or ash on the surface. The most important mineral constituents are quartz and silicates of various types, but mainly feldspars. Plutonic rocks solidify slowly, and are therefore coarse-grained, whilst volcanic rocks solidify comparatively quickly and become fine-grained, sometimes even forming glass. Depending on where the magma solidifies, the rock is given different names, even if its chemical composition is the same, as shown in the table (see Table 3) of main igneous rock types. A further subdivision of rock types depends on the silica content.

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Rock classification

After sedimentation, compaction and cementation of the mineral grains, a sedimentary rock is formed. If the sedimentary

rock is buried deeper and deeper under other rocks and sediments, the increasing pressure and temperature will cause re-crystallization, often combined with the formation of new minerals. A metamorphic rock is formed. At great depth in the crust the metamorphic rock will start to melt and form a new magma, and the cycle is completed.

GEOLOGY AND WHY IT MATTERS

Some sedimetary rock types Rock

Original material

Conglomerate

Gravel, stones and boulders, generally with limestone or quartzitic cement

Greywacke

Variable grain size from clay to gravel, often with angular shape

Sandstone

Sand

Clay

Fine-grained argillaceous material and precipitated aluminates

Limestone

Precipitated calcium carbonate, corals, shellfish

Coals

Vegetation in swamp conditions

Rock salt, potash, gypsum, etc

Chemicals in solution precipitated out by heat

Loess

Wind-blown clay and sand

Table 4: Typical sedimentary rock types and the material from which they originate.

Rock with high silica content is called felsic, and those with lower amounts of silica are called Ultramafic or mafic, also demonstrated in Table 3.

Sedimentary rock

Sedimentary rocks are formed by the deposition of material and its consolidation under the pressure of overburden. This generally increases the strength of the rock with age and overburden thickness, depending on its mineral composition. Elements of sedimentary rock are formed by mechanical action such as weathering or abrasion on a rock mass, transportation by a medium such as flowing water or wind and subsequent deposition. The origins of the rock will therefore partially determine the characteristics of the sedimentary rock. Weathering and erosion may proceed at different rates as will the transportation, affected by the climate at the time and the nature of the original rock. These factors will also affect the nature of the rock eventually formed, as will the conditions of deposition. Special cases of sedimentary rock include those formed by chemical deposition, like salts and limestones, and organic material such as coral and shell limestones and coals, while others will be a combination, such as tar sands and oil shales. Another set of special cases is glacial deposits, in which deposition is generally haphazard, depending on ice movements. Several distinct layers can often be observed in a sedimentary formation, although these may be uneven, according to the conditions of deposition. The layers can be tilted and folded by subsequent ground movements. Sedimentary rocks make up a very heterogeneous family with widely varying characteristics as shown in the table of sedimentary rock types, Table 4.

Metamorphic rock

The effects of chemical action, increased pressure due to ground movement at great depths, and/or temperature of a

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rock formation can sometimes be sufficiently severe to cause a transformation in the internal structure and/or mineral composition of the original rock. This is called metamorphism. For example, pressure and temperature may increase under the influence of up-welling magma, or because the strata have sunk deeper into the Earth’s crust. This will result in the recrystallization of the minerals, or the formation of new minerals. The change in mineral composition means that the new minerals are stable at the higher temperature and pressure. This occurs without melting of the original rocks, and little change in the chemical composition. A characteristic of metamorphic rock is that it is formed without complete remelting, or else they would be termed igneous. The metamorphic action often makes the sedimentary rocks stronger and denser, and more difficult to drill. As metamorphism is a secondary process, it may not be clear whether a sedimentary rock has, for example, become metamorphic, depending on the degree of extra pressure and temperature to which it has been subjected. The mineral composition and structure would probably give the best clue. Due to the nature of their formation (see Table 5), metamorphic zones will probably be associated with increased faulting and structural disorder, making efficient drilling more difficult. Metamorphic rocks are also characterized by new texture and structure. The reason for a change in temperature and pressure may be due to heat from intruding magma, or because the rocks or sediments have sunk deeper into the earth’s crust. Compression and tension in the earth’s crust also play an important role during the metamorphic stage. Metamorphic rocks make up a large part of the earth’s crust. They are divided into three groups, depending on the degree of metamorphism: low, medium and high. In the first group there are only slight changes in mineral composition. Typical low-grade minerals are chlorite, albite and epidot. At medium and high metamorphism many new minerals are

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GEOLOGY AND WHY IT MATTERS

Typical metamorphic rocks Rock type

Original rock

Degree of metamorphism

Amphibolite Mica schist Gneiss Green-schist Quartzite Leptite Slate Veined gneiss

Basalt, diabase, gabbro Mudstone, greywacke, etc Various igneous rocks Basalt, diabase, gabbro Sandstone Dacite Shale Silicic acid-rich silicate rocks

High Medium to high High Low Medium to high Medium Low High

Marble

Limestone

Low

Table 5: Typical metamorphic rock types and their origin, followed by the degree of metamorphism that is needed.

formed, for example, sillimanite and garnet. Due to the strong re-crystallization, all primary textures are destroyed, and in many cases it is very difficult to determine the primary rock. Metamorphic processes often make the rock denser and harder and more difficult to drill. Foliation is a kind of layering which is a characteristic feature of many metamorphic rocks. When rocks recrystallize under pressure from one direction, platy minerals like mica are orientated in layers perpendicular to the source of pressure. This results in banded or foliated rocks. Another type of metamorphic structure is lineation, where elongated crystals in the rock are oriented in the same direction, resulting in a cigar-like structure. Very often, the metamorphic rocks are named after the parent rock. Metamorphosed sedimentary rocks are called metasediments and volcanic rocks metavolcanites. Some examples of metamorphic rocks are given in Table 5. Quartzite is a very hard rock formed by the metamorphism of pure sandstone. Schist is a common metamorphic rock of medium to high grade. This rock is often named after the most common mineral, for example: mica schist; and chlorite schist. Marble is a well-known metamorphic rock formed from re-crystallized limestone. But there are other examples too of metamorphic rocks that, unlike the aforementioned, did not originate from sedimentary rocks. Igneous (magmatic) rock types can also undergo the process of metamorphosis. Gneiss is a high-grade rock type that is originally igneous rock which has undergone metamorphosis. In addition, as shown in Figure 4, gneiss is an example of how magmatic rock can skip over the sedimentary phase in the process of metamorphosis.

Macroscopic rock properties include slatiness, fissuring, contact zones, layering, veining and orientation. These fac-

Faults can consist of a single fracture plane, but it is more common that parallel fractures are created around a fault zone, which results in a shearing zone. Faults or fractures where the surrounding rock is crushed to small fragments are known as crush zones. The quality of the parent rock that will form the structure around the underground openings can be a major factor in determining the feasibility of a tunnel excavation, mainly because of their effect on the degree of support required. The tendency of rock to fracture, sometimes unpredictably, is also important to determine factors such as rock support requirements and the charging of peripheral holes to prevent overbreak. The procedures for minimizing overbreak and maintaining the contour design are strict and good results will yield benefits in terms of production and safety. Minimized overbreak will prevent the excavation of too much waste rock and a good contour preserves the structure and facilitates rock support. It is clear that rock structures, and the minerals they contain, can result in a wide variety of possible tunneling strategies. Obviously, the more information that is gained, the better the chances of success. If uncertainties occur in terms of unforeseen ground conditions and factors such as excessive water ingress, the advantages provided by modern tunneling equipment will be lost as drill rigs and other machines will be forced to stand idle. To avoid these situations it is vital to carry out an adequate amount of exploratory work to establish rock qualities in and around the site. Information from surface exploration drilling and geophysical methods of investigation are normally

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Rock classification

Macroscopic rock properties

tors are often of great significance in drilling. For example, cracks or inclined and layered formations can cause hole deviation, particularly in long holes, and have a tendency to cause drilling tools to get stuck, although modern drilling control methods can greatly reduce this problem.

GEOLOGY AND WHY IT MATTERS

Rock drillability is determined by several factors including mineral composition and grain size, hardness, brittleness and crystal habit, if any. In crude terms, rock compressive strength or hardness can be related to drillability for rough calculations, but the matter is usually more complicated. The Norwegian Technical University has developed the Drilling Rate Index (DRI), the Bit Wear Index (BWI) and the Cutter Life Index (CLI). The indices are determined by the rock properties, brittleness, surface hardness and wear capacity and are indirect measures for the drillability of rocks. The DRI is assessed on the basis of two laboratory tests, brittleness and surface hardness. The penetration rate can vary greatly from one rock type to another. It should be noted that modern drill bits greatly improve the possible penetration rates in the same rock types. Also, there are different types of bits available to suit certain types of rock. For example, Secoroc special bits for soft formations, bits with larger gauge buttons for abrasive formations, and guide bits, steering rods or retrac bits for formations where hole deviation is a problem. The BWI, or Bit Wear Index, gives an indication of how fast the bit wears down, determined by an abrasion test. The higher the BWI, the faster the wear. In most cases, the DRI and BWI are proportional to one another. However, the presence of hard minerals may produce heavy wear on the bit despite relatively good drillability. This is particularly the case with quartz, which has been shown to increase wear rates considerably. Certain sulphides in orebodies are also comparatively hard, impairing drillability. The macroscopic rock properties, visible to the eye, give engineers a first clue as to whether blastholes can be drilled with good results.

supplemented by probe or core drilling conducted from an underground position like a tunnel heading. Modern computer software can also assist with processing the vast amounts of data and to deduce the suitability of various excavation methods for the rock that is likely to be encountered.

Rock classification

In order to systematically determine the likely excavation and support requirements, the amount of consumables required, and whether a particular method is suitable, a number of rock classification systems have been developed. These are generally oriented to a particular purpose, such as the level of support required, stand up time for a defined opening, or the rock’s drillability. The methods developed to assess drillability are aimed at predicting productivity and tool wear. Factors of drillability include the likely tool penetration rate in proportion to tool wear, the stand-up qualities of the hole, its straightness, and any tendency to tool jamming.

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Another classification system being used by Atlas Copco is designated Diarot. It is aimed at calculating penetration rates and the bit wear for different rock types using a wide range of rock drills and tools. The rock parameters entered include unconfined compressive strength, brittleness and cerchar abrasivity index. Rock classification with respect to stability of openings plays a major role in all rock excavation and especially for underground projects. Commonly used rock classification tools are the Q-system (Barton et al, through the Norwegian Geotechnical Institute), Rock Mass Rating RMR (Bieniawski), and the Geological Strength Index GSI (Hoek et al). Bieniawski’s Rock Mass Rating incorporates the earlier Rock Quality Designation (RQD – Deere et al), with some important improvements taking into account additional rock properties. All of these give valuable guidance on the rock’s ease of excavation, and its self-supporting properties. In most cases, engineers will employ more than one means of rock classification to give a better understanding of its behavior, and to compare results. ◙

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GEOLOGY

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Rock classification

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Figure 1: Geotechnical investigations include methods such as seismic refraction, core drilling and sounding, to determine the quality of the rock mass.

A matter of priority Most civil engineers agree that the key to a successful tunneling project lies in the quality of the pre-study. That doesn’t seem to stop some projects from deviating from the budgeted construction plan. Proactive geotechnical investigations, without shortcuts, means fewer costly surprises. Whenever a new tunnel is to be built, and the tentative location, type and length have all been established, the first and most important step in the design process is the pre-study phase, which requires a variety of methods for geotechnical investigations. The purpose of the pre-study is to reveal the type and nature of the rock mass and ground that will be encountered during tunnel construction, the presence of fissured zones or fault lines that may create special technical challenges, joint fillings, hydrogeological properties, soil conditions such as soft clays, stresses and more.

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These factors are crucial in enabling the construction company to determine the most suitable excavation methods to use and to apply those methods in a way that will be effective, safe and meet the stipulated completion date. In addition, all of these factors combined will enable the company to build a cost calculation and establish a price tag for the contract.

Stepwise approach

As pointed out, having geological and geotechnical data available is a prerequisite when designing tunnels and caverns, which in turn calls for various field investigations and

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mapping to be carried out during the planning stage. The methods used and the extent to which investigations are carried out depend on the geology of the area and the type of project planned for. Subsea tunnels, for example, usually require more extensive, and thereby more costly, investigations compared with tunnels located on land where there is plenty of rock overburden. Geotechnical investigations are carried out in a number of steps. The advantage of this stepwise approach is that unworkable or unrealistic alternatives can be excluded before any extensive and costly investigations are initiated. In Norway, to mention one example, at least three steps are commonly followed. Feasibility study During the first step of the investigation, different ideas and possibilities are considered. The geotechnical investigation is usually limited, and its aim is often to find out if the project is possible and if it can be accomplished within reasonable costs. If satisfactory geological maps of the area do not exist beforehand, some geological mapping will be necessary at this stage. Seismic measurements or drilling may also be required, for example, in order to check if the rock overburden for the tunnel is sufficient. Principal design The recommended possibilities from the feasibility study are evaluated in detail, and a final location for the tunnel is selected for further planning. The main geotechnical investigation is now usually carried out, which is the goal of geological field mapping, seismic surveys, drilling, etc. Detailed geological maps and vertical sections are prepared and project costs are calculated, usually with an accuracy of ± 20%. Detailed design During this stage, the chosen project area is evaluated in detail. Accurate cost calculation is carried out, and construction drawings are prepared. Most of the geotechnical investigations have usually been finished prior to this stage, and only special attention is paid to individual zones, tunnel entries, etc. The tender documents are now prepared. The responsibility for conducting pre-studies and geophysical mapping falls on the shoulders of geologists and the exploration contractors they employ. The work is mostly performed by an independent firm of engineering consultants, except in cases of BOT contracts (Build Operate Transfer) when the construction company will probably choose to do the prestudy as well.

Field mapping

The field mapping method is employed at the initial stage of investigations and involves the careful study of all rock that is visible from the surface (outcrops) in a defined area surrounding the potential tunneling site. The purpose of field mapping is to provide a geological description based on rock mechanics data that is collected, including rock types, fissures and cracks. The results from field mapping will provide a general overview and a basis for more advanced investigations, such as geophysical measurements and drilling. For some smaller projects, however, field mapping may be the only type of geotechnical investigation that is required.

Geophysical measurements

From field mapping, it is only possible to observe the surface of any given outcrops, meaning rock that is visible from the surface. To get a physical picture of the underground, geophysics can also be employed with measurements that provide information on rock mass quality and the thickness of the overburden. A plan for geophysical measurements should be based on a geological map. The choice of method

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Rock classification

Pre-study investigations will normally involve the use of three methods: field mapping, geophysical measurements and drilling. It is also important to conduct desktop studies, which implies the search for documented information from previous projects and relevant sources.

Core drilling involves the use of diamond drilling equipment that extracts samples of rock in cylinder-shaped cores.

GEOTECHNICAL INVESTIGATIONS

N653KL N652KL N651KL

Figure 2: A wide range of geotechnical methods are often employed in combination, as shown in this 3D illustration. Coupled with data from various classification systems, the gathered information will result in tunnels being divided into different sections where individual rock reinforcement systems are planned.

for geophysical measurements will depend on the geological condition and need for exactness, which may change during the investigation, but the seismic refraction and reflection method is very common.

lacking. Using electrical measurements, it is possible to measure potential and current electromagnetic fields that occur naturally in the ground or that are induced by, for example, excavation work.

Seismic refraction is useful for the interpretation of the overburden for a tunnel. It involves the use of seismic transmitters and receivers, coupled with data processing hardware. This equipment is used to generate shock waves, and the various seismic velocities can be measured to enable an approximation of the geology and an estimation of the rock mass quality, even at great depths for deep-seated tunnels. However, the refraction method is not possible if the rock layers are reversed, in other words if soft rock layers are located underneath hard rock layers.

Variations in the resistivity of soil and bedrock produce variations in the relation between the applied current and the potential distribution as measured on the surface. This may reveal information concerning the composition, extent and physical properties of the subsurface materials. The resistivity depends on the pore water, which enables the porosity and fracturing of the rock to be determined. In this way, the electrical measurements can be used as a complement to or instead of seismic refraction during the geotechnical investigation phase for tunnels and caverns.

The accuracy of the seismic method depends on the placement of geophones and their spacing, as well as the direction of the seismic profile in relation to the geological structures. For best results, it is recommended that seismic profiles are placed in different directions. It is also good practice to measure the profiles both in parallel and at an angle to the tunnel line. When critical areas are indicated, such as soft rock or soil, exploration holes are drilled to verify the data that is

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Drilling

As geotechnical investigations are an expensive and time-consuming process, these are rarely performed at random. When it comes to drilling, two types of drilling methods are typically employed: sounding and sampling. By sounding the resistance of a drilled hole, the various soil cover layers and, their thickness and sequence can be determined, thereby indicating the

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GEOTECHNICAL INVESTIGATIONS

Probe drilling Electromagnetic survey Refraction seismic

N

Ground water level Core drilling

N651KL

N652KL

N653KL

CHAINAGE RMR Q-VALUE SUPPORT CLASS

0+000

1+000

2+000

3+000

4+000

Figure 3: A typical blueprint for a tunnel based on geotechnical investigations data and rock classification systems.

location of the rock surface. If more detailed data is required, such as rock mass quality, core sampling will be the next step, which involves the use of diamond drilling equipment that can extract samples of cylinder-shaped cores, collected in drill core barrels. Due to the increased complexity in tunnel designs, it is rare today that tunnels are constructed without core analysis in the pre-study phase. At the same time, core drilling is an expensive undertaking and should be planned carefully. Holes should be placed where they can give the most valuable information, especially in weakness zones.

Describing rock mass and ground conditions from a technical point of view is not an easy task. For this reason, engineers often prefer to use numbers rather than adjectives, which has led to a number of classification systems being employed around the world. They are instrumental in highlighting the parameters that are crucial for tunneling projects, and among the most commonly used systems are: • The Q system: Developed by Barton et al (1974) of the Norwegian Geotechnical Institute. The Tunneling Quality Index, also known as the Q system, was based on the evalu ation of a large number of case histories of underground excavations. It is widely used to determine rock mass char acteristics and tunnel support requirements from an empiri cal standpoint. The Q system expresses the quality of the rock mass in the so-called Q-value. • Rock Mass Rating (RMR): First published in 1976 by  Bieniawski, the RMR classification system focuses on the estimation of strength of rock masses, and it has since been refined as more records have been examined. A key benefit of RMR, as with the Q system, is that it provides an empiri cal study of fractured rock.

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Rock classification

Core samples are taken continuously along the hole, and in addition to samples, other reconnaissance testing is carried out, including hydrogeological measurements. Tests that measure the permeability of rock mass are of particular importance. If the rock quality is poor during sampling, core loss may occur. In these cases, video inspections of the drilled holes may be useful. The holes can also be used to reaffirm geophysical measurements and to conduct stress measurements. Rock stress has a direct impact on the stability of tunnels and caverns and can be measured in various ways. Overboring and hydraulic splitting are two common methods.

Classification systems

GEOTECHNICAL INVESTIGATIONS

Core samples must be retrieved in one piece to enable accurate analysis of the rock mass. Drill rigs used for this purpose usually feature a wire line device, or "core catcher" which lifts the core sample to the surface, eliminating the need to pull up the heavy drill pipe from the hole.

• Geological Strength Index (GSI): Concentrating on the description of two factors – rock structure and block surface conditions – the GSI system (Hoek et al, 1995) is used to estimate the peak strength parameters of jointed rock masses. In applying these systems, the rock mass is divided into a number of structural regions, and each region is classified separately (see Figure 2 and 3).

Continuous reports

After the contractor has been chosen, the construction period begins. In some cases there will be a need for supplementary geotechnical investigations during the construction period. This may involve drilling or geophysics data gathering ahead of the tunnel face to investigate rock overburden or weakness zones. In subsea tunnels, such investigations may be warranted as measurements from the sea can be difficult and expensive. Geologists usually work on the project during the construction phase as they continue to map the tunnel and provide advice regarding rock support and avoiding water ingress. A final report must always be prepared in order to sum up the experiences, which may be useful for future projects.

Unwanted surprises

If there is one thing that is rarely appreciated by tunneling engineers, it is geological “surprises”. Unexpected conditions

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during construction can turn a perfectly good project into a “nightmare” characterized by disruption in the workflow, tough technical challenges, higher costs and major delays, which may involve financial penalties. These surprises may also have a negative impact on safety, both for the workforce and also for nearby surroundings and structures. Yet there are countless projects carried out around the world each year that go “off plan” in one way or another. At worst, there are cases where reality has deviated on almost every level with the information provided by the pre-study. Today, experienced companies habitually build a margin for pre-study error into their calculations. The question is, can the reliability of pre-studies be improved?

Cost vs accuracy

One root of the problem lies in the way tunnel projects are designed and commissioned. In most countries, the principal is a public authority, typically a national transport administration or local roads and railways municipality. It is the public body’s duty to keep costs as low as possible in the interests of the taxpayer. The pre-studies commissioned by these bodies are often limited in time and budget, and engineering consultants are obliged to keep their work within these parameters. It is debatable whether this system is the best. In most cases where tunnelers have run into difficulties, pre-studies have been insufficient. In the hard rock region of

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GEOTECHNICAL INVESTIGATIONS

Scandinavia, for example, it is not compulsory to employ all three exploration techniques. Neither are there any rules that state that investigations must be made at specific intervals along the entire length of the tunnel. Lastly, there is little or no correlation between the total project cost and the amount of money that is allocated to the pre-study. Clearly, if only one million dollars is allocated to a pre-study for a project costing several hundred million dollars, it would be unreasonable to expect it to provide a very comprehensive analysis of the project site. Considering the huge disruption and additional costs that are caused by insufficient prestudies, another million dollars allocated to the pre-study would seem a small price to pay to maximize the reliability of the analysis.

Finding the right balance

Logically, the fewer geotechnical investigations that are carried out, the greater the unreliability and the higher the final cost of the project. To reverse this situation requires establishing a good balance between the extent and scope of exploration work commissioned and the size, complexity and cost of the project. When it comes to establishing the nature of the rock mass – which is the tunnel builders first and most important consideration – core drilling is undoubtedly the most reliable form of investigation. The problem is not as great when tunneling in urban areas as it is in the countryside and especially remote locations. In and around cities, there are usually many tunnels that have been driven already. Data from these projects is available, and although pre-studies must always be carried out, comparisons, assessments and reasonable assumptions can be made based on experience. In the countryside, on the other hand, where little or no information is available, extensive prestudies based largely on core drilling are a must. This is especially important at sites where the nature of the rock mass is notoriously unpredictable, such as in high mountain regions of the Himalayas, the Swiss Alps or the Andes. Here, extreme rock compression, squeezing ground, massive fractures, voids and other conditions can present extraordinary challenges.

When core drilling in confined spaces, the Atlas Copco Diamec 232 is a suitable option as it is small and flexible

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Rock classification

For example, it is essential that the specified shape and size of the tunnel – the tunnel profile – is maintained at all times. If the profile is deformed by squeezing ground, it will have to be recreated, and this means increased use of sprayed concrete, rock bolts and steel arches, which increases costs and work time. Core drilling is also the most viable method of exploring rock and soil in areas where a tunnel route is designed to pass under water. In this case, the drill rig is set up on land, and the drillstring can be steered to retrieve cores at angles beneath the bed of a river or lake and even take cores horizontally. ◙

y

x

Figure 1: When a tunnel opening is excavated, stress fields are redistributed in the surrounding rock.

Understanding how rock behaves

Constructing a tunnel in a safe and sustainable way requires a thorough understanding of the characteristics and behavior of rock and rock mass and how they respond to force fields in their physical environment. The science of rock mechanics is a complex world full of fascinating, natural phenomena. But for the modern tunneling engineer, it has just one purpose – to provide a platform for safe and sustainable reinforcement. The design of the rock support plan has three important criteria to fulfill. Firstly, it has to provide tunneling engineers with a safe environment in which to work. Secondly, it has to give the structure

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long-term stability so that it will be safe to use for many years into the future. And thirdly, it has to be economically viable. Rock, contrary to popular belief, is by no means inanimate; it is living material. In its natural, in situ state, rock is constantly moving and reacts in a variety of different ways whenever it is disturbed or disrupted by force fields. These changes can

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ROCK MECHANICS

be natural or induced by man through, for example, mechanical excavation. This means that tunnel planners and engineers are highly dependent on qualitative facts that underpin their decision making process regarding localization, dimensioning, excavation sequence and surveys of caverns, tunnels and shafts. Taking the right decision at the right time is paramount and will often have large economic consequences. To a large extent, this has been a driving force for the development of rock mechanics science. Rock mechanics provides a basic knowledge of the characteristics and behavior of rock and rock mass. But more importantly, it enables tunnel planners to evaluate how a given rock type, or different combinations of rock mass, is likely to react to various forms of excavation. The information regarding rock characteristics is gathered from rock samples. Altogether, the studies enable tunnelers to make a reasonably accurate assessment of the prevailing rock conditions that will determine the type of challenges that the engineers can expect to encounter during the excavation process. The fundamental issues to be addressed are: • Definition of the structural fabric of the rock mass, including aspects joints, faults and shear zones • Evaluation of the mechanical parameters of the intact rock and structures • Identification and quantification of the failure modes based on stress and structural analysis • Influence of the excavation sequence • Design of the rock reinforcement itself • Virgin stress situations • Water flow and water pressure

In situ and induced stresses

Rock at depth is subject to stresses resulting from the load of the overlying strata and from locked-in stresses of tectonic origin. When a tunnel opening is excavated, the virgin stress field is disrupted and redistributed in the rock surrounding the opening. (see Figure 1) Knowledge of the magnitudes and directions of these in situ and induced stresses is an essential component of tunnel excavation since, in many cases, the strength of the rock is exceeded and the resulting instability can have serious consequences for the tunnel openings.

Failure mechanisms

It could be said that stresses, rock strength and rock structures are the three most important factors affecting the stability of any excavation in natural strata material, and that a combination of various stress regimes, plus rock fragmentation and water pressure will dictate the excavation process. Tunnelers need a thorough grasp of ground conditions before rock support, such as bolting, can be installed in the best possible way.

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Rock classification

Rock stress intensity varies from very low to very high, and the discontinuity pattern varies from massive rock to small

ROCK MECHANICS

Heavily jointed rock

Jointed rock

Massive rock

Low stress levels

Massive rock subjected to low in situ stress levels. Linear elastic response with little or no rock failure.

Massive rock, with relatively few discontinuities, subjected to low in situ stress conditions. Blocks or wedges released by intersecting discontinuities, fall or slide due to gravity loading.

Heavily jointed rock subjected to low in situ stress conditions. The opening surface fails as a result of unravelling of small interlocking blocks and wedges. Failure can propagate a long way into the rock mass if it is not controlled.

High stress levels

Massive rock subjected to high in situ stress levels. Spalling, slabbing and crushing initiates at high stress concentration points on the boundary and propagates into the surrounding rock mass.

Massive rock, with relatively few discontinuities, subjected to high in situ stress conditions. Failure occurs as a result of sliding on discontinuity surfaces and also by crushing and splitting of rock blocks.

Heavily jointed rock subjected to high in situ stress conditions. The rock mass surrounding the opening fails by sliding on discontinuities and crushing of rock pieces. Floor heave and sidewall closure are typical results of this type of failure.

Figure 2: Stability challenges as a consequence of stresses and rock structure. Source: Support of Underground Excavations in Hard Rock, Hoek E., P.K. Kaiser and W.F. Bawden. 2000, Balkema.

cubic structures or rock that has high schistosity. Massive rock will possess most of the intact rock strength, but will also accumulate load and can fail violently under certain conditions (see Figure 2). Very fractured rock will tend to yield to stresses and often deforms in a problematic manner. It should also be noted that the shape, size, sequence and type of excavation affects the way rock and rock mass will respond and should be taken into account. Among the most common failure mechanisms are stressinduced failures such as tensile failure, spalling, shear failure and rock burst, and structurally controlled failures such as sliding along joints, crushing of joints or rotation of blocks. Tensile failure occurs when tensile strength is exceeded and stresses influence the rock mass in one or more directions.

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The failure is preceded by microfissures that later converge to form a complete failure area. This is manifested as a rough failure surface and is most common in walls in larger/higher rock caverns where the major principle stress is horizontal. Spalling occurs with uniaxial compressive pressure load and involves thin slices spalling in a direction parallel with the main stress direction. Splitting or cleaving is common in brittle, homogeneous rock that is exposed to high stresses. It occurs close to the tunnel’s boundary, normally in the roof in those cases where the main primary stress is horizontal. When structural rock failure occurs due to shearing, it is simply called "shear failure". This process is normally created by three axial loading. The failure starts with the activation of existing defects in the rock and the appearance of tensile failure fissures parallel with the principle stress line, similar to spalling. Rock burst is, in fact, not a failure mechanism by definition. Instead it can be defined as an induced seismic event as a result of tunneling (or mining) that damages the rock in excavated areas. A seismic event is the sudden release of potential or stored energy in the rock, creating a shock wave that causes damage to underground structures. In a wider perspective, the term rock burst is used as a collective description for failures that occur suddenly and in an explosive fashion. This form of failure normally starts with spalling, but the process is fast and often leads to considerable damage inside the tunnel. The phenomenon mainly occurs at great depth where the primary stresses are greater. For tunnels near the surface, seismicity and rock burst occasionally need to be taken into account when dimensioning, particularly when you have to deal with high horizontal stresses or excavation near steep slope surfaces. Sliding along a joint means that the shear stress exceeds the strength of the joint. Crushing occurs when the compressive stress exceeds the compressive strength. Rotation of the block takes place if the load induces a bending moment, causing a tensile stress in a joint with no tensile strength.

Gravity driven wedges

With openings excavated in jointed rock masses at relatively shallow depth, the most common types of failure involve wedges falling from the roof or sliding out of the side walls of the opening. These wedges are formed by intersecting structural features, such as bedding planes and joints, that separate the rock mass into separate but interlocked pieces. When a free face is created by the excavation of an opening, the restraint from the surrounding rock is removed. One or more of these wedges can fall or slide from the surface if the bounding planes are continuous or rock bridges along the discontinuities are broken, as shown in Figure 3.

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ROCK MECHANICS

1 2

3

1 2 3

Tunnel with small coverage area Coredrilling hole Tunnel with large coverage area

Figure 3: If bounding planes are continuous, or rock bridges along the discontinuities are broken, one or more wedges can fall or slide into the excavation area.

Figure 4: The size and shape of potential wedges depend on the shape and orientation of the openings.

Unless steps are taken to support these loose wedges, the stability of the roof and walls of the opening may deteriorate rapidly. Each wedge, which is allowed to fall or slide, may cause a further reduction in the restraint and the interlocking of the rock mass and this, in turn, will allow other wedges to fall. This failure process will continue until natural arching in the rock mass prevents further unravelling, or until the opening is full of fallen material.

techniques can be used in producing these calculations. The most common of these are:

The size and shape of potential wedges in the rock mass surrounding an opening depend on the size (see Figure 4), shape and orientation of the openings with respect to the orientation of the significant discontinuity sets.

Empirical design is based on experienced interpretations of the reinforcement need. This design technique should therefore be coupled to a system of rock characterization and/or classification as these systems are often based on several well-documented projects.

The stresses that exist in the rock mass prior to disruption in the form of excavation, are related to the load of the overburden rock and on the topography, but also on the rock masses’ geological history. Construction causes a section of the rock to be removed which leads to a redistribution of the stresses in the rock mass, and these new stresses depend on the stress conditions prior to construction. High stresses in the rock mass prior to disruption can therefore cause high stresses in the excavated area which may lead to failures. The stresses that occur in undisturbed rock are normally referred to as virgin (or in situ) stresses, while those that exist after disruption are called induced stresses.

In the tunnel planning, construction and management processes place different demands on dimensioning and several

• Empirical design and rock classification • Analytical calculation • Numerical models

Empirical modeling

The empirical technique can be used at an early stage in the project for designing the reinforcement and as a complement to analytical/numerical models. However, the empirical technique should always be complemented with analytical and numerical models for reinforcement design.

Analytical modeling

Analytical calculation can, for example, be based on relatively simple calculation models in order to estimate the required thickness of the sprayed concrete, taking into consideration the volume of the rock which can fall out between bolts, or in order to calculate the bolting requirement for securing loose rock fragments in the tunnel roof. Another example of an analytical calculation method is compressed arch in blocky rock mass and the Voussoir beam theory in blocky rock masses.

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Rock classification

Dimensioning

1 Tunnel with small coverage area 2 Coredrilling hole 3 Tunnel with large coverage area

ROCK MECHANICS

Using tools such as numerical modeling, stress regimes can be predicted and excavation sequences optimized.

Numerical modeling

In many cases, tunnel geometries or load conditions are more complex than the data that can be ascertained from analytical methods. Long term excavation planning can, therefore, benefit from detailed analysis such as numerical modeling and 3D visualization. Stress regimes can be predicted and excavation sequences optimized to keep the stress level at a comfortable level: not too high to create seismic events, and not too low to create major structural instabilities. Apart from being able to study more complex geometries, and to describe the various aspects of rock mass, various rock reinforcement elements can be included in the numerical modeling. These include bolts, sprayed concrete, concrete and more. In this way, the combined behavior of rock mass in a tunnel that has been reinforced can be properly analyzed. Numerical modeling can be used for both stress- and deformation analysis.

Follow-up and control

It is important to remember that dimensioning of, for example, rock reinforcement, cannot be regarded as complete until the tunnel itself has been completed. In other words, true

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verification of the bearing capacity is only possible during construction using observations, mapping, testing and measuring. Geological mapping should be carried out continuously throughout the excavation process. It should include rock mechanics information (e.g. via systems for rock characterization) and be complemented by visual inspections of the conditions in the tunnel, including the reinforcement. Testing of the support elements (e.g. pull tests) should be carried out according to specific programs which can be produced during construction. Monitoring of any deformations that arise during excavation provides a valuable opportunity to verify the dimensioning calculations and associated reinforcement design. If the deformations deviate from the projections, there is often a possibility to adjust the reinforcement work during the construction stage. A detailed measuring program should be established before the tunneling is started and the choice of excavation method should be guided by the extent of measuring that is required. ◙

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Rock classification

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Planning for new tunnels is a rigorous step-by-step process that requires a thorough knowledge of ground conditions, the excavation method, cost scenarios and potential risk factors.

A multi-phased process From conception through to construction, civil tunneling projects are developed according to a well-defined, multi-phased process. Meticulous attention to detail at every stage is a must to minimize the risk of costly errors when work gets underway. Irrespective of the type of tunnel to be constructed, a great many parameters have to be taken into consideration before work can begin, and this process must be allowed to take time to avoid errors and unnecessary costs further down the line. The process starts with the project owner who is responsible for defining the tunnel’s location, route and purpose. In most cases, the owner will also be responsible for carrying out preliminary studies to determine feasibility and potential methods of construction. This will result in a document that serves as a solid foundation for decision-making in the

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continued planning and implementation stage, including the procurement of suppliers and sub-contractors. At the next stage, the bidding process, tunneling contractors are obliged to demonstrate the same high level of planning integrity, in many cases even higher, in order to be considered for the contract to carry out the work. And their proposals need to be meticulously matched with the type of contract that is being offered. As shown in Figure 1, there are four contract forms that are common for most tunneling projects.

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TT3_1-Tunneling

PLANNING FOR NEW TUNNELS

PROJECT FLOW Proposal

Feasibility

Surveys

Construction Tender document documents

Bidding process

Construction

BOT (Build Operate Transfer)

DB (Design Build)

Turnkey

DBB (Design Bid Build)

Delivery

Testing

Delivery

Operation

Transfer

Delivery

Colored lines indicate the contractor´s responsibilities

Figure 1: The phases of tunnel construction and typical contract forms.

These are: • Build Operate Transfer (BOT): a joint venture whereby the responsibility for the detailed design, construction and financing is shared. The joint venture is given the conces sion to maintain and run the tunnel for a limited period and to generate income from operation of the tunnel. • Design Build (DB) and Turnkey: the design and construc tion are undertaken by a single entity known as the design builder, or design-build contractor. In both DB and Turnkey contract forms, the contractor is responsible for all of the work, including financing up until completion of the project. • Design Bid Build (DBB): a traditional contract form where by the project owner engages separate contractors and suppliers for the design and construction work. The DBB contract differs from the other contracts in several ways. For example, the delivery method is based on three main phases. These are, in order: the design phase, the bidding (or tender) phase and the construction phase. In this chapter we focus on the basic, multi-phased process that the tunneling contractor will generally need to follow, bearing in mind that these may differ due to local laws and practices.

Know the ground, know the method

The contractor’s main concern is with the type of geology through which the tunnel is planned to pass. Knowledge of the characteristics of the rock and surrounding ground conditions is crucial in order to select the most suitable method of construction.

The concept

Step one is to study the basic concept provided by the project owner. This will usually include an analysis of the motives behind the design, such as the need to speed up public transportation or expand municipal drinking water or wastewater treatment systems. Alternatively, the tunnel may be just one element within a much bigger development, such as to move surface-based power lines or parking lots underground, to free up land for housing, or to expand a hydropower plant or oil and gas depots. It may even be intended to form a section of a complex underground repository for nuclear waste. In addition to this, the concept will most likely include information on all known obstacles and challenges along the alignment such as mountains, rivers, bridges, geological fault lines, groundwater or underground structures and installations.

Surveying and feasibility

A crucial part of the owner’s pre-study work will involve geological surveys and ground investigations at the site. The purpose is to reveal the type and nature of the rock mass and ground that will be encountered, including the presence of fissured zones or fault lines, joint fillings, hydrogeological properties, soil conditions, and so on. These factors are crucial in order to establish the most suitable method and equipment that will allow the tunnel to be excavated effectively, safely and on time. The in-depth feasibility study will provide the basis for assessing the construction phase as it will detail

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The tunneling process

Most modern tunnel projects are normally developed stepby-step in the following phases: • The concept • Surveying and site investigations • Feasibility studies • Preparation of construction documents

• Preparation of tender documents • Tendering and bidding • Construction • Testing and delivery • Management and transfer (if applicable)

PLANNING FOR NEW TUNNELS

contractors will be required to complete in order to qualify to apply for subcontracts. Note that these questions to contractors will also be used to form the basis of the business relationships and types of cooperation that will later be proposed: i.e. they will act as the framework for the final tender application in which lead contractors are required to state which subcontractor structures and payment arrangements will be adopted in their bid. However, there are exceptions to this procedure depending on the contract form. If the tunnel project is set up as a BOT (Build Operate Transfer), a Turnkey project or a DB project (Design Build), the contractor will be responsible for the design and for developing the construction document.

Tendering and bidding

The tendering and bidding process may differ from country to country, but the procedure followed by most contractors is as follows:

A Boomer XE3 C drill rig on site during construction of the Goetschka Tunnel in Austria.

what needs to be done, stipulating all challenges and possible solutions. A wide range of methods is used to gather this vital information and the feasibility study is used as a reference throughout the planning stages. For more information on this, go to the section on geotechnical investigations, page 36.

Preparing the documents

When all of the facts have been ascertained, it is time to prepare the official documentation. Primarily this will consist of two documents: one to cover the project (Construction Document) and one for procuring subcontractors (Tender Document for contractors). The design phase and compiling the construction document is a complex process in which a great many technical details have to be incorporated and coordinated, including all of the findings of the geotechnical investigations. The final product will consist of technical descriptions and drawings, a bill of quantities (BQ), which details all materials, labor and their costs and is prepared by a quantity surveyor, as well as an extensive list of other related issues. The tender document for contractors will consist of the project description together with a list of questions that potential

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• Prequalification: understanding the project conditions (envi ronmental and technical demands, time schedule, start date, milestones, completion date, penalties, site visits etc.) It is common for contractors to ask for prequalification and this is done by supplying documentation on experience from similar projects. Listing of capacities in the form of equip ment and staffing may also be required. • Risk analyses: financial, contractual, technical and geologi cal risks. • Project planning: how to proceed in light of the demands and risks, how the project will affect third parties, what capacity is required to meet the time schedule, what type of equipment is required, size of the crew. • Procuring estimates: subcontractors, material such as rock bolts, sprayed concrete, tunneling equipment, spare parts, service contacts, etc. • Estimating the project: content of the tender, prices, time schedule, description of the works, company SHEQ (Safety, Health, Environmental, Quality) document, resources, per sonnel and equipment, reference projects, alternative solu tions besides the tender document, tender bond. • Standard evaluation criteria: cost, technical description, project plan, organization, resources, environmental plan. • Negotiation: signing the contract, project startup. Attention to detail and accuracy cannot be over-emphasized in these steps and a rule of thumb is to do everything correctly from the beginning. This goes for developing the organization, selecting the methods, highlighting the demands placed on the company and informing the crew of their tasks so that they know what will be expected of them. When it comes to procurement, contractors should be wise in making purchases. It is advisable to look into the total cost of the project instead of at the individual unit prices. Suppliers

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PLANNING FOR NEW TUNNELS

should be chosen carefully. Awareness of delivery times for equipment is crucial must be specified and the total cost of ownership should always be taken into account.

Starting up the construction

Once the contract has been awarded and construction is due to get underway, it is imperative that good planning discipline remains in place. What’s important at this stage is to ensure that the actual construction will adhere to the specifications of the contract with regard to time, cost and quality. To achieve this with as few deviations as possible, it is necessary to make sure that uncertainties and unpredictabilities can be dealt with swiftly and smoothly which, in turn, requires excellent cooperation between the project owner and the contractor. Experienced and skilled staff on both sides is also a must. Production needs to be planned in both the long and short term, purchasing plans for equipment and materials should be in place, and plans for the procurement of the necessary labor should be clearly defined.

Testing and delivery

Once the project is complete it will have to undergo a period of inspection and testing. Any observations or issues that may arise from the official Completion Inspection must first be addressed before delivery and final payments can take place. The contractor normally has to provide a guarantee period of a certain number of years, at the end of which there will be a Guarantee Inspection. Again, any issues arising from the Guarantee Inspection must be addressed, after which the contractor has no further obligations. Contract types vary when it comes to final delivery. For example, if the contract is based on a BOT (Build-Operate-Transfer) agreement, the tunnel will also be operated and managed by the supplier organization for a period of time, often three years, before being finally transferred to the principal owner.

Prerequisite for success

One prerequisite that will have a major impact on the outcome is the selection of equipment. The contractor that chooses to use tried and tested methods with equipment from recognized manufacturers with a solid track record in tunneling will be much more likely to win the contract. Conversely, the contractor that chooses to use equipment that may not be entirely suitable or wholly reliable is less likely to be successful.

Tunnelers celebrate the main breakthrough at the Lötschberg Base Tunnel in Switzerland.

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The tunneling process

It is important to add here that the choice of equipment is not only a matter of which drill rigs, loaders, rock bolts and ventilation systems to use. It is also a matter of obtaining the best package that will also include parts and services and experienced technical support in order to achieve the highest quality at the lowest total cost of operation. ◙

Every tunnel project is dependent upon a well-organized operation. This includes having skilled and trained personnel and a transparent flow of information, among other key factors.

Big wheels in motion People and teamwork are the keys to excellence in all tunnel projects. Having a solid operational framework in place is of the utmost importance, well before the very first hole is drilled. On time, within budget and a first-class result – the three-fold definition of successful tunneling can only be fulfilled with elaborate teamwork at every step of the way and where safety is also an ongoing and natural part of the process. Although it is true that the development of modern technology is changing the face of the tunneling industry day by day, people remain the most valuable asset of tunnel projects large or small and regardless of complex designs. Each team involved is an indispensable link in the chain that drives the great wheel of progress from day one to final delivery. As

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such, it is important to emphasize that it only takes one missing link to jeopardize the schedule, resulting in increased costs. For this reason, it is important for project managers to begin the work of allocating personnel and setting goals at the earliest possible stage. Organization is about building a strong base for cooperation at every level by making full use of communication techniques that are at the heart of teamwork. This needs to be backed up by good training. Trained, skilled operators and technicians perform better, find their work more enjoyable and contribute to increased productivity. They

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MANAGEMENT OF PROJECTS

know how to maximize the output from machines in a safe and sustainable way.

Sustainable workplace

Much like solving a puzzle, tunnels are constructed in a stepby-step process over extended periods of time in a confined and sometimes difficult environment. A tunneling site could involve anything from 20 people to more than a thousand in larger projects that involve several tunnels, with key functions spanning everything from drill and blast or TBM operators (Tunnel Boring Machine), tunnel designers, coordinators and surveyors to site superintendents, project managers and engineers for installations. To maintain a smooth operation, work procedures should be established well in advance of the first construction phase before the clock starts ticking in terms of schedules and costs when, generally speaking, every delay weighs the operation down. As a first step, a few fundamental parameters need to be established and adhered to including: • A safe working environment • Transparent flow of information • Trained operators and service personnel • A well-organized overall operation, including workshops/ maintenance • Employee development at local level • Readiness for unforeseen events A completely trouble-free tunneling process may well be a rare occurrence. Having said this, keeping staff members informed about the project’s mission, their roles and ongoing developments is a proven approach that boosts the positive odds considerably. Good communication through clear messages is a guiding principle that should permeate the entire organization. By focusing on clarity when designating assignments, you will avoid any overlapping of duties and tasks, which means reducing the risk of costly double-work. Furthermore, high-level information flow is far more likely to foster a spirit of participation among the team and enthusiasm for the task at hand.

Proactive culture

at the tunnel face. At the very least, a sustainable workplace will result in benefits such as less turnover of staff (satisfied people stay), the potential to develop an experienced organization, better control over risk/cost factors, and a foundation for long-term customer/supplier relations. Being proactive is also a crucial aspect of safety, which today is a constant concern for all construction companies. Safety is not something to be focused on now and again or whenever it seems appropriate. It is a never-ending process based on a desire for continuous improvement in order to safeguard the lives and well-being of tunneling professionals. A raised awareness about safety issues over the past decade has also had a large, positive effect on productivity levels.

Cyclical workflow

A high competence level is usually the most important factor for satisfactory completion of tunnels. This not only goes for site personnel but also for external contractors and sub-suppliers. At regular intervals, the entire team should be engaged in operational tracking by answering basic questions such as

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The tunneling process

In addition to strong communication, flexibility is recommended such as giving staff the possibility to influence the setup of daily routines. Another key element is to offer training on a continuous basis, leaving no one doubtful of their skills and capabilities. Experience shows that setting high goals, instilling a sense of shared purpose and showing consistency in management will stimulate a proactive culture. This means that challenges in the construction cycle can be dealt with more quickly and with a minimized impact

Continuous training intervals is a proven way of boosting safety and efficiency at the worksite.

MANAGEMENT OF PROJECTS

Operational tracking and assessment is increasingly carried out during construction, together with all personnel. This helps to identify SHEQ issues (Safety, Health, Environment, Quality) and alternative solutions to specific challenges.

what has been achieved, what the problems related to SHEQ issues (Safety, Health, Environment, Quality) are and how alternative solutions can be found, as well as the challenges in short term vs. long term planning. Once the above guidelines have been put into practice, a cyclical workflow can be introduced. This implies that everyone involved is both aware and well-prepared for the next step at any given moment in the tunneling process. Operational tracking also serves the purpose of boosting overall transparency at the worksite. It is increasingly common for tunnels to be assessed during their construction as this facilitates accurate backtracking of weakness zones and how they have been handled. Without this information, it will be much harder to plan for continued maintenance of sensitive areas as these may have been covered with a concrete lining prior to the tunnel becoming operational.

QA/QC protocols

Although each tunnel design is unique, setting high benchmarks for quality is a prerequisite for today’s high demands on tunneling projects. Greater understanding yields higher quality, and both drilling and rock support tend to be two major focal points. A driller, for example, needs to be not only fully prepared but also aware of his or her impact on the

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quality of blasting, which, in turn, affects haulage operations. In addition, project managers should engage dedicated teams who can perform quality checks on a regular basis. Quality control (QC) is the term applied to a company’s own efforts to make sure that rules, specifications and best practices are adhered to and that promises to customers are duly delivered. Regular input and approval, however, is also needed from independent auditors. While universal QA/QC protocols are often adapted and tailored to fit the needs of individual tunnel assignments with their distinct challenges, there are a few important points that are generally followed. Checking of written routines, follow-up on routines, data gathering regarding all processes and tasks, economic followup on maintenance and tracking of Key Performance Index (KPI) are just some examples of important aspects. As clients are placing higher demands on the design and quality of tunnels as well as production processes and health and safety standards, which form the basis for ISO certifications, QA/QC programs are indispensable tools for future success in the industry. To conclude, a holistic approach and a cyclical workflow should be the overarching goal of an organization. It is the mechanism by which quality becomes a natural part of the overall operation, which maximizes the potential for meeting delivery targets. ◙

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The tunneling process

ATLAS COPCO UNDERGROUND CONSTRUCTION – TALKING TECHNICALLY

The Atlas Copco range of simulators provides a realistic on-site experience based on a wide variety of training scenarios.

A smarter way to go New equipment and new technologies put high demands on tunneling staff, regardless of their knowledge and skills. Getting equipment operators trained and fit for the challenge has never been easier. The importance of training can never be overemphasized. Trained personnel perform better, find their work more enjoyable and contribute to increased productivity. Having well-trained operators also increases overall safety in the workplace, which considerably reduces the risk of accidents and injuries. Familiarity with today’s high-technology methods is a basic requirement of all tunneling engineers, and some equipment manufacturers such as Atlas Copco offer a wide range of training programs to provide them with the skills they need. These days, the same requirements are also being placed on equipment operators who are not only expected to operate

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their machines correctly and safely, but also required to have a broader understanding of their role in the process and the personal contribution they make to the success of the company they work for. The reason for this is twofold: the need for high productivity at the lowest possible cost and the fast pace of technological development which is constantly increasing requirements on contractors to offer the latest tunneling solutions. Against this background, no tunneling contractor today can afford to put an expensive piece of equipment, a drill rig for example, into the hands of an operator who is not fully trained for the task.

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OPERATOR TRAINING AND SIMULATORS

Simulators for skills shortage

In the past, skilled labor was available in abundance. New recruits were relatively easy to find and were traditionally trained by the most experienced operators on the crew. Today, there is a worldwide shortage of skilled labor. New recruits are extremely hard to find and it is becoming increasingly difficult for contractors to find people on their own staff who can spare the time to train new recruits. This problem is being addressed in different ways in different countries, but the common goal is to find a solution that does not burden ongoing operations. In this context, the use of simulators for training purposes instead of real equipment and, to a great extent, outsourcing the training responsibility to external specialists are emerging as the smartest way to go.

The power of simulators

The advantages of this approach are considerable. Firstly, simulator training enables operators to be trained without disturbing ongoing projects or having to assign experienced operators to the job. Secondly, operators can be trained on the surface where they can learn and practice in an environment without disturbance from other activities. And thirdly, it eliminates having to put new operators in charge of expensive, high-technology equipment until they are fully qualified to take on such an important responsibility. This reduces the risk of machinery being damaged due to incorrect use and, more importantly, it can reduce the enormous costs associated with disruption to operations, time-out for unscheduled maintenance and repairs and, last but not least, accidents resulting in injuries to personnel. Another big plus is that trainees do not need to worry about the challenges of handling machines in a tunneling environment – with all the potential hazards that this involves – until they are sufficiently skilled and confident.

Tailor-made programs

The actual cost of training new recruits can be minimized since the training time required when using simulators can be substantially reduced. According to studies, training with simulators cuts the time it normally takes to get new drill rig operators up to speed by an average of 50%, which is a big advantage in terms of increased efficiency and operational capacity.

step-by-step courses to teach operators all of the skills they need in order to take full responsibility for their Atlas Copco equipment.

Virtual reality – a fun way to learn

The simulator part of the program has been especially successful. Here, the trainee operator gets exactly the same look and feel of the real machine. All procedures such as startup, drilling, tramming, drill plan handling and positioning are performed in exactly the same way as the real machine, giving a totally realistic experience. Another important advantage is that simulators are capable of producing and analyzing performance data, enabling trainees to improve their own performance and compare results with their fellow trainees in groups. This not only produces higher standards but is also a fun way to learn. Trainees can also go back and repeat any aspect of their training at any time, either to refresh a specific skill or to improve on weak areas. The range of such training simulators now available on the market is consistently expanding and in time will encompass most types of equipment for underground construction. In the future, as learning devices such as these become more widespread, contractors will be able to train new operators to a high standard with a minimal impact on their day-to-day operations and resources. And this, in turn, should impact on flexibility, productivity, safety and profits. ◙

MASTER DRILLER PROGRAM The Atlas Copco Master Driller program is a program that provides trainee drillers with theoretical and practical training in three steps. It combines e-learning or classroom training for basic knowledge and skills, as well as simulator training for practical, true-to-life learning in a variety of mining scenarios. This is then followed up by on-site training with an Atlas Copco specialist. After successfully completing all three levels – Bronze, Silver and Gold – the trainee is awarded a Master Driller Diploma.

Master Driller provides trainee drillers with three levels of proficiency – Bronze, Silver and Gold – and consists of

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The tunneling process

Recognizing the need to address the training issue, a number of equipment suppliers have been proactively developing their own tailor-made training programs to offer to their customers. A typical case in point is Atlas Copco’s Master Driller program, which is specially designed to match all of the equipment in the company’s range.

Well-placed and proper installations for water, compressed air and electricity go a long way to keeping tunneling projects on schedule.

A worthy investment for progress

To drive a tunnel is a tough job and basic components such as roads, electricity, ventilation and water are more than just essential requirements. Experience shows that good quality infrastructure is money well spent. Whether for roads and railways, hydropower plants, water and utility tunnels or underground storage, a reliable and well-maintained infrastructure is the lifeline of any tunnel construction. What is meant by “infrastructure” in a tunneling context? The answer is everything that is a fundamental need, including roads and ditches, electricity, water supply and waste

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systems, ventilation, lighting, compressed air, communications technology and rescue chambers, to mention a few. Although some tunnel projects are more complex than others, all benefit from early investments in all of the above. The infrastructure is simply expected to function correctly from day one, and should any of these fundamental elements fail, the entire project will suffer in terms of lost time and cost.

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WORKSITE INFRASTRUCTURE

Which equipment will be used and how will it be powered? How much water will be needed or pumped out? How much ventilation is needed and where in order to guarantee a safe working environment and minimize equipment downtime? As soon as a project moves from the tender phase to real calculations and planning, the answers to these questions can never be left in doubt.

Road maintenance

Good quality roads that are well maintained play a large role in achieving high utilization at the tunnel face. If roads are not dry and up to the desired standards, equipment will most likely be damaged, resulting in costly unplanned maintenance, and drivers and operators may well be put at risk. This means that the flow of construction traffic will be impaired by a slow mucking out process that not only breaks the time schedule but is potentially very costly. When constructing a road network, the choice of material should be made according to the site conditions. In nearly all environments, a well-packed road and a well-maintained ditch are necessary to ensure proper water drainage from the road body. If there are leakages from the tunnel roof, these should be prevented by grouting or by installing a drainage system leading the water down to the ditch. This is crucial because dripping water will eventually destroy the road surface and lead to expanding potholes and cracks. In access tunnels where frequent transport takes place over long periods, it can be well-invested money to surface the road with concrete asphalt, especially if there are steep inclinations or sharp curves.

Water supply

Most of the processes in tunnel construction, such as drilling, concrete spraying, grouting and bolting, require a continuous water supply and a wastewater management system. If either of these are wrongly designed, low pressure and poor water flow will result in a negative effect on progress at the tunnel face, especially with drilling. Supplying the right amount of clean water is often a challenge due to environmental issues.

The highest demand for water usually comes from drilling. One way of reducing consumption is to use water mist on

In addition to electricity, water and ventilation, compressed air is a required utility used for water mist during drilling, among other applications.

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The tunneling process

Here, it is highly recommended to recycle waste water in a treatment plant, which requires a thorough knowledge of water needs. Without an accurate design of the sedimentation system, particles that are too big will pass and damage the equipment. The treatment plant must also be set up according to existing environmental regulations.

WORKSITE INFRASTRUCTURE

R CHESCU AM E BE R

Figure 1: Rescue chambers must be strategically placed. Pipes, wiring and ducts must be installed professionally, fixed securely on roofs and walls.

the drill rig, a system where air and water are combined. Although water mist requires a bigger compressor, water consumption can be reduced up to 95%.

parameters, including ventilation, pumping systems, workshops, offices, the simultaneous use of equipment and more. It is also important to devise the electrical system so that it can handle peak load.

Waste water

In order to avoid any damage to the system, all cables, transformers and conduits must be located safely in the tunnel system. They need to be protected from both water leakage and from other moving equipment.

A well-designed waste water system handles both process water and any ingress of water from the surrounding rock and the surface that flows in via the tunnel openings. When designing the system, all the inflow criteria must be included and a pump chain should be installed with overcapacity in order to account for wear and tear of the pumps. It is important to consider the potential impact of a malfunctioning pumping system or a lack of extra pumps. Experience shows that excess water may not only flood the tunnel face but also destroy roads, with huge repercussions in terms of increased costs.

Electricity system

Power supply is another fundamental factor. The electrical system must be designed to take into account all consumer

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Communications technology

Instant and effective communication is a prerequisite for short lead times between activities and in order to uphold steady progress at the face. In tunneling, this involves many types of installations such as radio communication, WLAN, tracking systems for personnel and equipment, and mobile telephony. The radio system is usually the primary tool for tunnel personnel to communicate with each other. It can be either an analog or a digital system, whichever suits the project best, so that help can arrive rapidly should any process go wrong or an accident occur. Access and tracking systems are instrumental for knowing which personnel and equipment are present

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Figure 2: Poorly installed infrastructure leads to insufficient air flows, leaking pipes and potential hazard, resulting in delays and increased costs.

at any location, at any given time. These systems not only address emergency situations, but also help to increase the utilization of manpower and equipment. In a tunnel project, a continuous flow of data is transferred between equipment and people. This means that a reliable WLAN system is highly advised, which can also be used to manage the other communication tools mentioned above.

Compressed air supply

Looking at history, compressed air has mainly been required for handheld pneumatic drilling equipment, concrete spraying and ANFO charging. This, however, is gradually changing as hydraulic equipment in tunneling is increasingly employed with the water mist function, which is dependent on a certain supply of compressed air.

Comprehensive planning

Adopting a meticulous approach is crucial when setting up the infrastructure for a tunnel project. Eventual scenarios in the construction process must be scrutinized and calculated in order to avoid mistakes early on. For example, site managers need to assure that rescue chambers, electricity and water supply sources are not placed too far from the tunnel face. All it takes for costly downtime to occur is for an electrical cable to fail to reach a socket or equipment unit. Similarly, short distances are highly recommended for stockpiling materials, such as spare parts, drill bits, rods and bolts. Here, as the excavation progresses, it may be possible to take advantage of niches previously created for haulage equipment or rescue chambers. All available space near the production area should be utilized to its full potential. ◙

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The current trend is to have onboard air compressors mounted on modern equipment, to avoid large compressors and pipelines underground. When external air compression is used, compressors are often located outside the opening and are connected to a system of steel pipes in the tunnel system. The air system should be mounted in a way that reduces the

risk of damages to the pipes. A badly maintained or damaged system results in insufficient air flow and pressure, as well as increased costs. The same applies to ventilation ducts, see chapter "Ventilation systems: Optimizing the air", p. 116

Taking a proactive approach toward service can make the difference between successful, on-time delivery and costly delays.

Preventive maintenance for maximum uptime

Keeping a close eye on your equipment’s wear and tear is an indispensable part of the tunneling process. This is where effective planning and reporting systems will have a striking effect on rapid action for any items that require attention. There is widespread appreciation among modern construction companies for the role of preventive maintenance and the impact it has on quality, safety, operational costs and delivery times for tunnel projects. This has become especially apparent in recent years with the constantly increasing level of technology associated with rock excavation equipment coupled with the growing scarcity of skilled labor. Preventive maintenance as a means of achieving maximum equipment uptime, avoiding unnecessary disturbance to

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operations and reducing costly downtime is beyond dispute. The high availability of equipment that this provides is crucial for project reliability, which enables construction companies to follow their plans and meet their targets. As in many other industries, maintenance is equally important when it comes to facilities and infrastructure. Roads, workshops, ventilation, electricity, water supply, filtering systems and all other components in construction projects need continuous attention in order to safeguard productivity

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Maintenance of equipment should be as calculable as possible. All service data should be factored into the operational cycle of tunneling projects.

and provide a reliable, safe working environment. Although it is fair to say that a great deal of progress has been made globally in this area, there remains ample room for improvement.

Quality in all areas

In order to achieve maximum efficiency in service and maintenance, it should not be regarded as an isolated function but rather as an integral part of a process in which all components interact. The ability to monitor equipment performance and automatically compile statistics on wear and tear has enabled companies to optimize their service arrangements. This information highlights where the primary problem areas lie and enables preventive measures to be initiated efficiently and cost effectively. Simultaneously, the training of maintenance technicians has improved as more and more suppliers develop professional on-site training programs for their customers.

Maintenance planning

In order to capitalize on preventive maintenance processes and reduce disruptions to operations, contractors should ideally implement an efficient planning system with reliable data mapping. This, in turn, requires strategy and organization. The objective is to make maintenance and service as calculable as possible where precise outage time of all equipment can be counted into the tunneling operational cycle. A maintenance organization should always be established in accordance with the excavation strategy. It should measure key performance areas, maintain detailed records, and take into account everything from emergency breakdown repairs to planned component replacements and all preventive maintenance hours with the specified procedures.

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The tunneling process

With the development of more advanced underground equipment offering longer service life, the nature of maintenance work has shifted from repairs to component replacement. Removed components are often transferred to surface work-

shops for repair, and in some larger tunnel projects, contractors will utilize niches in access tunnels as temporary service bays. In addition, more and more suppliers of rock excavation equipment are offering full service agreements whereby expert maintenance service is provided on-site, 24 hours a day, 365 days of the year, allowing the customer to better focus on their core activities. On-site visits from maintenance experts and product specialists are a trend that is expected to continue.

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machine interruptions and 2 h external interruptions, the calculation will show the following:

Calendar time Planned idle time

Planned operational time

Preventive maintenance Machine interruptions

Available time External interruptions

Utilized time

Figure 1: Typical interaction between calendar time, planned operational time, available time and utilized time.

Whatever the underground project may be, benefits for both parties can be obtained from employing a system that includes the following: • Ratio of production vs. maintenance • Mechanical availability data • Equipment utilization • Mechanical reliability • Service tracking of components • Cost and trend reports • Backlog Management • Labor key figures Calculating the planned availability of equipment is an efficient way of achieving full capacity production at a tunneling worksite. In order to optimize the preventive maintenance cycle, a number of definitions and distinctions are normally adhered to, including the following: • Preventive maintenance: planned on a regular basis • Machine interruptions: unplanned downtime due to techni cal malfunction of equipment • External interruptions: operational downtime due to factors unrelated to machinery, including unforeseen ground condi tions, environmental issues, damage, complaints or logisti cal problems • Availability: percentage of planned operational time when the machine is available • Utilization: percentage of calendar time when machinery is in operation (utilized) • Stock availability according to long-term plan To illustrate with an example: of a 24-hour calendar time with 1 h of planned idle time, 1 h of preventive maintenance, 0.5 h

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Availability Available time / Planned operational time = (24-1-1-0.5) / (24-1) = 93.5% Utilization Utilized time / Calendar time = (24-1-1-0.5-2) / (24) = 81.3% As shown in Figure 1, preventive maintenance is essential in order to secure maximum machine uptime and is particularly important for tunneling projects where automated or semiautomated processes are employed, such as blasthole drilling. It is also important for contractors to monitor and follow up on maintenance needs; how, when and why it is performed; and the results that a chosen system yields. A few basic requirements will include answers to questions such as: • Is there a clear division of responsibilities? • Are processes, procedures and instructions established and clear? • Are the targets and KPIs clear to all involved? • How are monitoring and reporting performed? • Is there a documented review process? • Is there an organized system for making improvements? In general, service and maintenance facilities for large tunnel projects are located on the surface in between site offices and the main access tunnel or worksite entrance. A rule of thumb is to find a strategic location at a safe distance from haulage routes yet in close enough proximity for maintenance to be carried out with maximum efficiency. Workshops need central power and water supply, lube stations and pump systems. It is also important that chemicals are used carefully and material safety data sheets (MSDS) are provided in an accessible location for all personnel. An approved process must be in place to respond to any possible liquid / chemical spillages and spill kits must be in place in suitable locations. The chosen storage location for liquids / chemicals should in no way pose a risk to the surrounding environment.

Statistical data and logistics

To achieve maximum equipment uptime, it is advisable to look at the whole tunneling process preferably using a maintenance planning software system that is synchronized with performance data for all machinery used at the worksite. Statistical data should be used to follow-up, eliminate bottlenecks and establish the most favorable conditions, including a well-drained, dry, safe and sustainable work area that also aids in the maintainability and lifecycle of cables and other sensitive equipment components. In addition to machine maintenance, road maintenance should be an ongoing process and should be regularly reviewed to

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Adopting procedures for preventive maintenance means that spare parts can be ordered in good time, which minimizes the impact of equipment downtime.

prevent major work on roads as well as machines. For example, when it comes to haulage operations, a well-maintained road will allow for safe and efficient transport of excavated rock from the tunnel face and reduce wear and tear factors on equipment, such as vehicle tires, transmission and suspension systems and frame components.

In this way, the forecasted requirements on service and maintenance both now and in the future will be sustained, which in turn will allow for the operation to better meet its planned production targets. ◙

PEAK PERFORMANCE Adopting a scheduled maintenance program is the best way to ensure that tunneling equipment is performing at optimum level at all times, thereby minimizing downtime, keeping productivity levels high, and avoiding costly repair work. Atlas Copco offers comprehensive and tailor-made service agreements for all its rock excavation equipment, covering everything from drill rig components and parts to rock drills and drilling steel.

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The tunneling process

For more information, please visit www.atlascopco.com

The Atlas Copco Boomer range is often used in drill and blast tunneling. It is equipped with a Rig Control System (RCS) so that vital drilling data can be monitored at a distance.

Seeing the big picture The ability to oversee the performance of an entire fleet of tunneling machines during operation is now a reality, offering significant improvements to productivity and efficiency. The possibility to monitor the performance of mobile tunneling equipment from a central point and in real time has been explored for many years. Not only would project supervisors be able to keep individual machines under constant surveillance, they would also be able to monitor their performance, identify potential problem areas and quickly react to any potential disruption in the excavation process before it occurred. The information could then be processed and correlated to create a truly proactive service and maintenance program that would result in considerable savings in terms of reduced downtime, increased productivity and faster completion. To many tunneling engineers, remote monitoring is still a thing of the future, but that doesn’t mean it is not available. On the contrary, a number of equipment suppliers have developed a variety of well-functioning systems, not least Atlas Copco,

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whose proven Rig Control System (RCS) on tunneling rigs enables key data to be gathered, stored and analyzed on a continuous basis.

The next level

Atlas Copco has now taken this capability to the next level in a joint venture project with the automation and power company ABB. The project, called Mobile Machine Integration, enables all of the collected data to be available at one single control center, representing a significant step towards largescale integration of tunneling equipment into a process control environment. Mobile Machine Integration brings together ABB’s long experience of automation together with Atlas Copco’s cutting edge systems for capturing, transmitting and presenting

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machine data from mobile equipment. As a machine works and moves around underground, relevant information is collected by the on-board data system and transmitted wirelessly via WiFi access points to a local server. This data is then available to be displayed and analyzed in a variety of ways, as shown in Figure 1, on a standard computer screen and via a web interface, including all the vital parameters that are displayed on, for example, a drill rig’s display screen, including pressure flows, penetration rates, temperatures and more.

Adjusting parameters

To gather machine and production data is the main objective of monitoring. Another important function, however, is to be able to track all operations online so that the entire tunneling process can be controlled with as high efficiency as possible. As in all industrial production processes, unforeseen events may occur which is why it is an invaluable resource to be able to adjust parameters and set new priorities from one central location, with as little human intervention as possible. For optimized results, the Mobile Machine Integration system should be used with computerized equipment such as drill rigs, loaders and trucks equipped with Atlas Copco’s RCS technology. The RCS rigs are prepared for communication not only in terms of available data on the machine but also for standardized protocols such as IREDES (International Rock Excavation Data Exchange Standard). The technology can be applied to older machines too although this will mean that only a limited range of data will be made available and shared during operations.

Real-time data

Having access to real-time data regarding the status, location and activities of the equipment fleet allows for much greater control over the tunneling process. For example, a real-time alert indicating a delay in one process allows for the tunneling schedule to be altered immediately, thereby minimizing any flow-on effects. Similarly, real-time alerts regarding machine operational issues can be sent directly to the service department and acted upon immediately to prevent machine failures.

Figure 1: The Atlas Copco Certiq system is a base component of Mobile Machine Integration. It enables real time monitoring of production data, alarms and warnings, as well as the availability of drill rigs, loaders and trucks.

This enables potential mechanical failures to be predicted and averted, and idle machine time to be turned into productive time. Similarly, bottlenecks in the production process or ineffective work processes can also be identified and analyzed by the system. Mobile Machine Integration is designed for the harsh, underground environment where wireless infrastructure may well be less than perfect. It is also scalable, accessible from anywhere and can be easily integrated into other systems. At the same time, infrastructure such as fiber networks and antennas need to be installed in a good way to keep the system alive, using rugged components. With civil construction and tunneling in particular under increasing pressure to optimize processes and reduce costs, monitoring technology of this kind is an ideal beginning. In time, step-by-step developments will make it possible to observe and track all activities underground from one centralized control room. ◙

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The tunneling process

In short, having real-time information regarding the status of a tunneling fleet allows operators, supervisors and managers to make informed decisions on how to handle potential problems or disruptions before they occur, rather than after. The positive impact of real-time information on operational performance and cost is enormous. If the system indicates that a drill rig is reaching a critical point in any area, an alarm is raised. The supervisor can then alert the drill rig operator directly and, for example, issue an instruction that the rig must be delivered to the service workshop.

The control central gives tunnelers a bird's eye view of operations with real-time data for drilling, haulage, ventilation and other key tasks.

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Portal access tunnel Access tunnel Main tunnel Service gallery

Figure 1: During the construction phase, the access tunnel makes it possible to advance the main tunnel from several headings. When the project is completed, it can be used as a service tunnel.

Tunnels – a prerequisite 1 Portal access tunnel 2 Access tunnel 3 Rail tunnel 4 Service gallery

for a connected society

The construction of tunnels for roads and rails continues to be a major contributor to the development of the modern society with advanced technology making it easier than ever to accomplish. If the wheel is the most important invention in the history of mankind, the tunnel is surely not far behind. In fact, it is often argued that it was the advent of the tunnel, which made it possible to travel through mountains, that is the key to all progress and development. In our modern times, few would deny the incredible contribution that has been made by the telephone, the Internet or mobile telephony in terms of connecting people around the globe. But nothing compares with the physical ability of

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tunnels to carry huge numbers of people or goods from one place to another, often over long distances, and through seemingly inaccessible terrain. Furthermore, the role of the tunnel in the development of today’s society shows little sign of abating. Urbanization continues to grow exponentially across the globe, and with that the need to locate mass transit systems underground, along with increasing pressure on infrastructure networks, both domestic and cross-border.

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How it all began

The earliest recorded tunnels, such as the one beneath the River Euphrates in Iraq that dates from about 2 200 BC, were built for pedestrians. They were generally short and just large enough for one adult male to walk through. In more recent history, in the latter part of the 1700s and early 1800s, tunnels were built as conduits for canals, enabling barges loaded with goods to pass between towns and cities through difficult terrain. However, in October of 1829, everything changed when thousands of people descended on the tiny English village of Rainhill in the UK, halfway between Liverpool and Manchester, to see five steam locomotives compete against each other over a distance of 56 km (35 miles). Stevenson’s “Rocket” famously won the contest, achieving a top speed of 48 km/h (30 mph), hauling 13 tonnes. Stevenson picked up a check for GBP 500 as well as a contract to start building locomotives for the Liverpool and Manchester Railway – and the rest is history. What’s significant about this milestone is that prior to the advent of the railways most people in the UK lived and died within a radius of just 15 miles of their home. Within 20 years of the Rainhill Trials, however, a network of railways had been developed that made it possible for every working man to afford to travel. The impact was felt across the world. Continents opened up and the industrial revolution gained huge momentum in the 19th century. By 1850, there were no less than 8 000 km of railway in operation in the UK alone (see Figure 10 p.76). But there was a problem. Railway tracks could only be laid on very gentle slopes and bridges and tunnels had to be built to carry the tracks across valleys and through hillsides. However, bridges and tunnels were expensive, which is why most older railroad lines have quite narrow curves and many bends.

Two thirds of existing rail networks were built before the 20th century. The majority of these have been upgraded since the 1960s.

To create rail connections between central and southern Europe, it was necessary to build tunnels through the Alps. Many of these were built at high altitudes and the trains had to negotiate many bends on the climb up to the tunnel entrances. Figure 11 (p. 77) shows the construction date and location of some of the biggest early Alpine tunnels.

Construction began in 1973, and since it was designed for fast passenger trains as well as for express freight trains, its maximum incline is a mere 1.25%. Combined with the hilly terrain, however, it runs through 61 tunnels and over 10 large bridges. Of the total length of 327 km, 120 km are through tunnels. The line was opened fully in 1991 and the standard speed is 250 km/h (155 mph), although 280 km/h is permitted if a train is running late.

Road tunnels

Obviously, road tunnels used by pedestrians and horse-drawn carriages have a much longer history than rail tunnels. The number of early road tunnels far exceed those used for railways, but it was not until road transport using automobiles soared after World War II that the demand for higher road standards began to increase. To meet those demands, major

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Underground construction

By the end of the 19th century, more than two-thirds of the currently existing railway lines had been built. This means that the majority of the lines being used as late as the 1960s did not allow for high speed trains due to the alignment standard for grades and curves applied at that time. Since then, many stretches have certainly been upgraded, both without going underground but also into tunnels. As the roads improved and cars and trucks started to compete with the railways and to a certain extent, air transport, it became clear that a major upgrade of the rail network was a must. The alternative was that rail transport would continue to decline and eventually die out.

A good example of an upgraded railway is the new Hanover – Würzburg line in Germany. This was the first of several highspeed railway lines to be upgraded for Inter-City Express trains and, at 327 km long, it is also the longest railway line in the country.

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Figure 2: Underground road and rail tunnels are essential in cities with high population density, where metro lines are also integral to the mass-transit system.

improvements were made from the 1970s and onwards, and in many locations throughout the industrialized world, roads went underground. These tunnels were built in urban areas to ease traffic jams – The Periferic around the city of Paris is a good example – and in rural areas with intense traffic to overcome major shifts in altitude, such as the Eisenhower Tunnels in the Rocky Mountains in North America. In addition, road tunnels were built wherever it was cheaper to go underground than to build on the surface, such as the second Tomei highway in Japan between Tokyo and Nagoya. The decisions that determine the upgrade or creation of new traffic routes, are largely taken by national and local government authorities and often involve extremely large investments. As a rule, decisions to build new routes only become politically viable when the existing traffic situation has reached unbearable proportions for the citizen. There are models for estimating the advantages of creating new traffic routes, where time savings for the user and added value for communities, with respect to an improved environment, are two of the biggest plus points. To facilitate this decision-making process, some roads, tunnels and bridges are

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financed by toll payment systems. Other financial solutions used to make major traffic installations come to fruition are the so-called Build, Operate, Transfer projects (BOT). In this case, venture capital companies and contractors form joint ventures to provide the necessary finance and then take the income from the toll over a defined number of years, after which they hand it over to the local government administration. A typical example of a BOT project is the express rail connection between the city of Stockholm, the Swedish capital, and its international airport, Arlanda. This is a line that includes some major tunnels as well as an underground station at the airport terminal.

The underground option

One way of overcoming traffic jams is to give citizens the option of a fast public transport system underground. Very few cities with a population of less than half a million are able to enjoy the advantages of a metro, and there are many cities with a population of over one million that still do not have one. This means that the first metro will inevitably have to be built in congested areas with all the difficulties and costs this involves. A case in point is the New Dehli metro where some of the central parts have now been completed. When the time comes to expand into the suburbs, the additional metro

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Because of its fjords and mountainous terrain, Norway has over 1 000 road tunnels totalling more than 800 km. The tunnel shown above, Glaskartunnelen, is 592 m long.

lines will simply be natural extensions of the existing infrastructure. Another important issue is to consider where road or rail tunnels should be located. The majority of rail tunnels are located in urban areas where metro lines also constitute a large part of the mass transit system (see Figure 2). Regular rail tunnels and stations, not only those for metro lines, have become viable solutions over the past few decades. One example is the new lower level of New York’s Grand Central Station, with the eastern access crossing the East River underground.Another example is a new, extremely large underground railway station complex now being constructed in Stuttgart, Germany. The new railway line that runs between Copenhagen, Denmark, and Malmö, Sweden, is also, in large part, placed underground. Metro lines, on the other hand, are naturally located in the most densely populated areas.Road tunnels have not only becom an important part of the transportation networks within cities. Many of the ringroads that circumvent traffic around the cities are also, to a large extent, placed in tunnels.

The Plabutsch tunnel in Graz, Austria, is an excellent example of this. It was during the 1970s that it became obvious that traffic could no longer be permitted to run through the 1 000 year old city. But the question was where to locate the new highway. After a long and protracted debate, it was decided to place as much as 10 km of the new road in a tunnel through a cliff that borders on the suburbs, west of the city. An alternative to this plan was to place the highway even further westward on the other side of the Plabutsch mountains. There was a 15-year gap between the construction of the first and the second tunnel. To some extent, this confirms the belief that new roads and tunnels are normally only built when the traffic situation becomes unbearable.

Different methods

The mechanical breaking of rock by means of a Tunnel Boring Machine (TBM) is one method of building tunnels. Here, the full tunnel section is excavated in one operation. The machine, or TBM, is designed to tackle the prevailing rock conditions which in most cases means that it is best suited for excavation in one type of ground. Without

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Underground construction

In addition, there are several examples where major arteries through cities have been rerouted underground. The relatively new Boston city tunnel is a good example. In addition, it has also become increasingly common to reroute traffic that

previously ran through the city centers to the city outskirts via tunnels.

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equal conditions. This means that the TBM method is preferable for small-size tunnels due to its high speed. Long tunnels are also suited for mechanical excavation as they offer more tunnel meters on which the depreciation of TBM gear can be distributed. That said, the opposite is true for the drill and blast tunneling method. Road and rail tunnels must be considered as large tunnels with cross-sections that are seldom smaller than 60 m2, with the exception of metro tunnels that may be as small as 25 m 2. On the other hand, even metros must have closely located stations that require the cross-sections to be enlarged. In those cases, it is common practice to excavate the running lines by TBM and develop the wider sections at the stations by conventional drill and blast.

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In weak ground formations and in city centers the station may be excavated by the road header technique in order to eliminate disturbance from blasting operations. Choosing between these two excavation methods is far from easy, and it is not uncommon to employ both techniques at the same construction site. Conventional excavation by drill and blast is preferred by many due to its flexibility in dealing with the variations in both tunnel cross sections and ground conditions. However, it is more demanding in terms of skills as the technique of mechanical excavation is easier to learn. For more information on TBM vs. Drill and Blast, see chapter "Choice of methods" p. 174.

Excavating the face

Figure 3 and 4: To achieve a faster advance rate in wide openings, top heading excavation and benching can be conducted simultaneously. In short and large tunnels, the top heading is excavated first.

going deeply into the technique of excavation by TBM, it is important to understand the circumstances in which the TBM method is preferred. The excavating tools on a hard rock TBM are the so-called disc cutters that create a circular cutting path on the tunnel face. Each disc has its own path and the paths are concentric. The cutters are limited with respect to the load they can take and the speed at which they can roll. This means that the outermost cutter located on the rotating head determines the machine’s rpm. The consequence of this is that the larger the diameter, the lower the rpm. The advance rate of the heading is, therefore, dependent on how deep the cutters can penetrate the rock with each revolution and the number of revolutions per minute. In principle, a 4 m diameter machine will advance twice as fast as an 8 m diameter machine when operating in

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Excavation of full section or just partial sections is an issue for all large tunnel excavations. Today, drill rig suppliers offer rigs that can cover cross sections up to 200 m 2 in one setup at the face. So limitations on excavated face area are rarely a problem for the tunnel builder. The reason for splitting a large face might be the rock quality. A large face may not be able to stand up long enough to allow for the required rock support to be installed. In single-track tunnels, being some 8.5 to 9 m high and 6.5 to 7.5 m wide, full section excavations can normally be achieved even under poor rock conditions. One example of this is the Lötschberg base tunnel in Switzerland, which is some 40 km long and was excavated by both TBM and the drill and blast method. The latter was preferred by the client in sections with poorer ground conditions, which, incidentally, dominated this project. The rock conditions along the tunnel route were classified into five groups, each with a defined amount of rock support to be installed and defined lengths of the rounds. In none of the support or excavation classes were the single-track tunnels given a split section. The length of the rounds were set to make it possible to install the required rock support in due time to avoid the ground surrounding the opening from loosening. For blasthole and

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bolthole drilling, three-boom drill rigs were used, assisted by two-boom rigs operating behind the tunnel face. By maintaining the same invert level throughout the excavated tunnels, a mucking system using continuous conveyors turned out to be an attractive hauling solution. In wider underground openings, such as road tunnels where simultaneous excavation on two levels is possible, this excavation concept is applied on longer tunnels since, in many cases, it gives a faster advance rate when considering the whole tunnel section. The principles are shown in Figure 3. In shorter and larger tunnels, it is seldom worthwhile to start the process of simultaneous top heading excavation and benching. In these cases, the top heading is excavated all the way through, as shown in Figure 4, followed by the excavation of the bench.

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In wide sections, 15 m or more, the top heading itself is split into two or three headings. The reason for this may be a fear of instability when opening up a very large face in ground conditions that are characterized as weak rock. By splitting the face, rock support can be installed without jeopardizing the stability. Splitting of the top heading face in large underground openings with good rock conditions may also be the case. Multiple faces offer a better opportunity to utilize the equipment that is allocated for the tunneling work, and a better utilization gives higher flow of rock out of the tunnel or cavern. Cavern excavation is a form of tunneling but with essentially larger dimensions. Here, the tunnel width is in the range of 20 m and the principles for multiple heading excavation can be seen in Figure 5. They should be at least a couple of rounds. For a better understanding of what large underground openings may require when the rock material is weak, or has a swelling characteristic, the excavation sequence for a three-lane road is shown in Figure 6. When deciding on which type of excavation approach to take, the details of the excavation process have to be established. The process itself holds a number of sequential operations and these are shown in the sequential diagram shown in Figure 7. In this case, eight activities are involved, although the number of activities may vary depending on ground conditions and the demands of the design. For example, the mucking may have to be carried out in two steps in order to apply the sprayed concrete support as soon as possible to secure the stability of the face area. Step one in mucking is to give access to the heading for the concrete spraying equipment. In order to achieve this, roughly onethird of the muck has to be shifted.

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Figure 5 and 6: The principle of multi-heading excavation for large underground openings, typically 20 m wide or more. Bottom illustration shows the excavation sequence for a three-lane road in weak or swelling rock.

Overbreak and support

The process of minimizing the overbreak and support starts with the drilling of the blastholes. The hole diameters are normally in the range 43 to 52 mm, where probably 45 mm is the most commonly used. There is a trend towards larger hole diameters as they offer the opportunity to go for larger diameter drill rods that are stiffer. Stiffer rods tend to give less hole deviation, which is very important for the economy of the excavation. In civil construction for road and rail tunnels, it is of great importance to stick to the lines and grades given in the design documents. Overbreak means excavation beyond the stipulated contour. The majority of rail and road tunnels around the world are given a two-layer support with a primary layer applied in the face area which is good

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Another example is that pre-grouting may be required for sealing the ground and that drilling for grout holes and grouting will have to be carried out, although normally only for every third round.

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ROAD AND RAIL TUNNELS

rigs for civil tunneling are capable of locating the blasthole collaring point with an absolute accuracy of less than 10 cm. This is achieved by having the drill rig position established with an accuracy of 1 cm.

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EC

EC

Bolting

Drilling and Surveying

Concrete spraying

Charging

The position of the rig and its angle to the tunnel axis are registered by use of total station readings utilizing fixed points back in the tunnel and fixed points on the rig itself. For the actual face to be drilled, the valid cross section and drill plan are stored in the rig’s onboard computer. This means that the rig knows exactly where to collar the hole as well as the drilling direction. In addition, the rig’s boom arms and joints are programmed to follow the directives from the computer. However, it is not possible to be more exact than the given figure due to inaccuracies mainly in the mechanical systems.

Scaling

Blasting

Mucking

Ventilation

Figure 7: The sequential operations performed at the face in tunneling.

enough to stabilize the rock at least during construction and, in many cases, much longer.The secondary support is often an in situ concrete lining and the two layers are meant to have a service life of 100 years, sometimes more. This lining has a very accurately defined inner contour. The space between the rock surface and the inner contour of the lining has to be backfilled with sprayed concrete and concrete. This means that all overbreak has to be replaced by concrete or sprayed concrete, which is very costly for the tunnel builder. To spend major efforts on hole-drilling accuracy of the contour holes is something that usually pays off. Stiff drill rods which give only a minor hole deviation, are a low cost way of reducing the amount of overbreak. Accurate contour holes are not only economical for the builder, but also have significance for the rest of the holes in the round. An accurately drilled cut (start of the blasting) means, in most cases, a good pull of the round. A good pull gives an excavated length that is 92% of the drilled length or more. The majority of the holes are normally located in the cut and along the contour. The latter are closely placed, allowing the amount of explosives used to be considerably reduced, and this is meant to give a nice, straight cut of the rock between the holes and, consequently, limited overbreak. Accurate hole drilling also means that the holes are being positioned in the right place along the hole length. Modern drill

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To quantify the advantage of investing in a technically advanced drill rig with the Rig Control System (RCS), in comparison with an older type, it can be said that the additional investment is paid back after less than 2 km of tunnel with a cross section of 70 m 2. This is due to the savings on sprayed concrete that can be realized when using a price of USD 150/m3 and USD 300/m3. The blasting agent is normally of a bulk type since it is easier to charge as hoses are used for pumping the explosives into the holes. The cheapest type is ANFO, but more and more users are going over to emulsions as these can cope with wet holes in a far better way. A more advanced way of using the emulsion is to apply the string loading technique. This technology offers the possibility to partially fill the holes. This means that one type of explosives can be used in all holes and the explosive strings are given weight variations adapted to the position of the holes. The periphery holes are normally given the lowest weight/m hole. For more information see chapter charging and blasting, p. 130.

Mucking out

Mucking of the rounds is almost always conducted by use of a regular wheel loader. In road tunnels holding two lanes and curbs, the width is in the range of 9 to 11 m. This gives good opportunities for loading of trucks right up at the face, using the standard way of tipping the buckets into the truck bed and fairly big loaders. In rail tunnels, the situation is somewhat different. The width of the single-track tunnels will not allow larger wheel loaders to dump the bucket into trucks in the conventional way (pin on). One option is then to arrange loading bays at defined distances and perform the loading, as shown in Figure 8, which is a common way to do it in smaller tunnels. Another option that has become attractive is to equip the loader with a bucket that can be tipped sideways (see Figure 9).

ATLAS COPCO UNDERGROUND CONSTRUCTION – TALKING TECHNICALLY

ROAD AND RAIL TUNNELS

This offers the opportunity to load the trucks right up at the face. At longer haulage distances, which might be the case in rail tunnels, the use of a conveyor might be an attractive alternative. For more information,chapter "Loading and haulage", p.158. To be able to send the blasted muck on the conveyor it has to be crushed into smaller fractions. A mobile crusher, therefore, has to follow the advance of the tunnel heading at a distance of 50 to 100 m. The crusher is fed by side-dumping wheel loaders, but other alternatives are also viable such as continuous muckers, e.g Häggloader.