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• Viji Thulasiraman

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Introduction There are a number of fairly common techniques available that allow grass to be incorporated into a pavement to provide 'the best of both worlds', ie, the appearance of grass but the load bearing capability of a well-constructed pavement or driveway. They can be utilised in those areas where the hard permanence of a typical pavement might be undesirable, such as in conservation areas, roadside verges, emergency services access, canal towpaths, farm tracks or rural settings, and they are also used for erosion control in some situations, although the specification and type of system(s) used can be completely different to that outlined below. Different proprietary systems provide varying ratios of hard-pavement to grass, and the best system for any given project will need to take into account these differences. Some systems can only be installed by specialist contractors, while others can be installed by competent workmen or even diy-ers. It should also be noted that special grasses ought to be selected for planting the various systems, as most ordinary seed mixtures are unlikely to be sufficiently hard-wearing to withstand being trafficked. A few suggested seed mixtures are given further down the page. he 5 techniques considered on this page are:o o o o o

Hopsack Paving Spaced Paving Cellular Paving Reinforced Turf Mesh Protected Turf

All these techniques rely on a sub-base to give the paving its strength, although the types of sub-base recommended will vary with type of system chosen, existing ground conditions, and anticipated usage. A typical construction detail for each technique is given below.

Hopsack Paving This is the simplest of the 4 techniques, and utilises readily-available, plain rectangular concrete paviors, laid to a pattern that leaves significant 'holes' or 'pockets' that are filled with soil and seeded. This technique can be used for residential driveways, or in the garden. For path use in a

A Hopsack pattern created from standard 100x200mm block pavers, giving 50x50mm pockets for soil.

garden with reasonably firm and stable soils, the sub-base can be omitted, but be prepared for the bricks to move. Any rectangular blocks can be used to create a hop-sack pattern resulting in varying sizes of 'pockets' in the finished pavement. The edges of a hopsack pavement sill need to be solid, either against an existing sound structure, such as a wall, or with an edging unit or soldier course laid on concrete, as described on the Block Paving Page.

For residential driveways, patios and paths, a 100mm sub-base is usually sufficient (see Subbase Page), but heavier loads, such as large vans, may need 150mm thickness. For trackways, car-parking areas etc., consult a paving contractor or civil engineer for specific advice.

Once the blocks have been laid, the pockets should be filled with a well-draining, friable soil, or soil/sand loam, and compacted as for normal block paving. It's worth spending a few quid, if necessary, to get a decent planting medium, as the grasses will have only this small pocket of soil to survive upon for the next few years. The soil in the pockets can be seeded immediately with the selected grass mixture, although the soil will settle over the ensuing weeks and may need 'topping-up', or it can be left to settle for 4-6 weeks and topped-up prior to seeding.

The relatively small proportion of grass to each square metre of this type of grass paving make it less reliable than other techniques, and there is a tendency for the grass to die off within a couple of seasons, but it does have its uses, and, if fed with a liquid fertiliser and watered in dry weather, it can look quite attractive in the right situation. Typical Hopsack Paving construction detail

paced Paving This technique again relies on commonly available block paviors, that are laid on a prepared sub-base and bedding layer, with 'spacers' between adjacent blocks giving a wide, but consistent, joint, that is then filled with the selected soil prior to seeding. Different manufacturers have different proprietary systems, but they all utilise a square or rectangular 'standard' block with some form of spacer, often plastic, approximately 3045mm wide. The number of spacers per block is determined by intended usage (more spacers used on trafficked areas) and type of block. Full instructions will be supplied by the spacer/block manufacturers.

Aquada Paving System by Marshalls

Again, this technique can be used for driveways, paths, patios, and, with a more substantial sub trackways, car parks and other large-scale, low traffic-speed sites.

The choice of block, and the width of the joints, determine the ratio o paving, and this allows this ratio to be manipulated, by choosing large blocks, to suit individual site requirements.

For example, using 240x160mm blocks with 35mm joints results in ap grass by area, whereas using 160x160mm blocks, this ratio becomes joint by area. Typical plan layout of spaced paving showing spacers being used to create 30-45mm joint between 240x160mm blocks

Again, soil and seed need to be carefully selected, before filling the joints, and the grass should establish itself before allowing vehicular traffic to use the pavement.

Grass does seem to survive better in the joints of spaced paving than it does in the small 'pocket paving, and, along with feeding and watering in dry spells, it may even need the occasional atten mower.

Cellular Paving See also Cellular Systems Page This is the most widely used type of grass-paving, and is claimed to be structurally sounder and than other forms. Basically, specially-shaped, interlocking 'cell' pavers are laid on a prepared be over a sub-base, and the 'cells' filled with the chosen soil and seed. There are a good number of systems available, in 3 formats; pre-cast concrete cells, plastic cells, and cast in-situ concrete ce Different proprietary systems have differing bedding layer requirements, and you will need to check with manufacturers whether their system requires a granular, a grit sand, or a sand/soil bedding layer.

Sigma block fromBrett

Turfstone by Tobermore

enerally speaking, these pre-cast concrete units are laid using the same methods as outlined on the block paving page.

This technique is suitable for all but the very heaviest applications. The scale of the project, and its intended use, will determine the best system to be used. Some manufacturers are not equipped to cope with orders of less than 300m², although it may be possible to arrange for a local builders' merchant to obtain a smaller quantity. These systems are quite popular with local authorities looking to provide hard-standing or emergency access to otherwise 'green areas', such as pumping stations on residential estates, and access trackways for service vehicles, fire engines, etc..

12 month old GrassGuard system

Established GrassGuard system

Grasscrete® is a proprietary system that relies on placing disposable plastic 'pots' at equal spaces over a prepared base and then pouring concrete to fill the spaces in between the 'pots', which act as temporary formers for the eventual pavement. Once the concrete has hardened, the flimsy plastic pots can be removed, and a selected soil mix used to fill the resulting voids. The soil can then be seeded. Grasscrete® is a proprietary system that relies on placing disposable plastic 'pots' at equal spaces over a prepared base and then pouring concrete to fill the spaces in between the 'pots', which act as temporary formers for the eventual pavement. Once the concrete has hardened, the flimsy plastic pots can be removed, and a selected soil mix used to fill the resulting voids. The soil can then be seeded.

Grasscrete Paving

Grasscrete slab with temporary plastic formers

Some systems allow gravel, decorative aggregates or bark to be used to fill the cells in place of the more usual grass, and some manufacturers will supply cells ready-turfed if required. Filled with a gravel, these plastic cells can bring stability to an inclined access way, and help minimise the inevitable drift of the gravel to the bottom of the slope. Plastic cell matrices (as they are sometimes known) are considered in more detail on a separate page.

Grass-filled plastic cells

Gravel-filled plastic cells

The type of system chosen dictates the grass:hardpaving ratio, with some thin-walled plastic cells, offering up to 94% grass surface, rendering the structural elements virtually invisible, while others, such as the pre-cast concrete units that are available, make a feature of the cell shape, which is usually rectangular or hexagonal. All of these cellular systems have been specially developed to ensure that the grass can and does survive, so much so that they can sometimes become overgrown if not tended regularly. Indeed, some systems are so successful at nurturing a natural overgrowth that they have been used on SSSI and sensitive heritage projects.

Grass paving at Stirling Castle

recast Concrete block systems The grass jointing is essential to the structural integrity of such systems. Where grass growth is absent or poor, the individual blocks have a lowered resistance to differential movement when trafficked. In regularly trafficked situations, this can result in sub-base pumping via the gaps between the individual units. Firm edge restraint is essential as any rooting through to the sub-base will be tenuous at best and the units will spread under load. Castellated or studded systems can be difficult for pedestrians as the soil fill within the units settles under vibration or is washed from the surface, leaving a protruding 'stud' which presents a significant trip hazard.

GC Group's Grassblock

Plastic systems (HDPE and Polypropylene)

GC Group's Grassroad pavers, before and after

Only really suitable for low-speed occasional use. The relatively thin depth of these systems and their inherent flexibility can result in 'trampolining', where the units 'bounce' when trafficked. This can turn the surface into a quagmire in regularly trafficked areas, such as carparks. The trade-off for a higher ratio of grass cover is a reduction in tolerance to wear and loading. Should not be used on gradients where slip resistance is essential.

In-situ castings Each job can be individually designed according to traditional slab design methods to ensure competence and adequate drainage control. No differential settlement or lateral spread, so no need for edge restraint. The only system suitable for vehicular loads of 40 tonnes.

Other considerations Gravel fill is acceptable in low-traffic situations, but hoggin should never be used as it will 'set' and kill off any grass. Where reinforced grass paving is used for Fire Path access, special note should be given to the subbase, which can quickly become saturated. Erosion Control by GC Group

Reinforced Turf This is a comparatively new development and, as far as I can ascertain, there have been only a few case studies of this type of technique, but it does have its admirers, and there will most probably be a small, but steady, market for it. The basic principal is that a specially selected grass is grown on a geo-membrane, which is then laid over a prepared bedding layer and sub-base. The sub-base provides the strength and stability, while the geomembrane holds the grass layer together.

Manufacturers claim that this type of system can be used for most normal, low traffic-speed applications, although whether it will ever be developed and promoted to the sports industry or the general public remains to be seen. This system ensures 100% grass coverage, and the usual maintenance, such as feeding and mowing, will need to be undertaken on a regular basis. The life-time of this system is an unknown quantity at the time of writing, but should be good for 10 years. There are also reinforced turfs developed specifically for erosion control, rather than trafficking, and are beyond the remit of this site. However, Some of the manufacturers listed on the links page also supply these 'erosion control mats', and their technical departments will be more than happy to help you with your queries.

Tensar Mat® by Tensar International

Mesh Protected Turf This system is becoming quite popular with those responsible for overspill car-parking and pedestrian usage at occasional events, with groundsmen looking after areas of lawn, and with caravan/leisure parks, where the natural appearance of grass with the load-carrying ability of a pavement, all at a minimal cost and with little or no construction work required, is very appealing. The basic premise is that a tough polypropylene or HDPE mesh is laid over an area of turf or grass, and this allows foot-traffic, low-speed cars and vans to use the area without completely ruining the grass. The mesh may need to be anchored to the ground at regular intervals by means of ground pegs, to prevent slippage and to help disperse the loads. The mesh works to protect the grass roots from being damage, to minimise 'pumping' of wet ground, and to avoid rutting of soft spots.

Turf Protection Mesh by Tenax Ltd.

The soil type, the type of grass/turf cover and the level of protection required will determine the best mesh to choose for each application, and the better manufacturers have dedicated technical teams to help in identifying the best solution.

Grasscrete, a Bomanite Pervious Concrete System, is a cast-in-place, monolithic, pervious concrete pavement that is continuously reinforced to provide superior structural integrity. Bomanite Grasscrete is the green alternative to standard concrete surfaces providing a variety of landscape solutions while maintaining a sustainable green product design used for emergency access lanes, delivery access routes, overflow parking areas, and for intermittent drainage channels that help prevent erosion. Grasscrete has been a Bomanite System for over 20 years with installations throughout North America in all climate types. Achieved through the use of two differing techniques and three differing tools known as “formers”, Grasscrete is void structured concrete – a pervious pavement system that can be cast using proven mix designs with no potential for freeze-thaw or clogging issues. Grasscrete can be used as an exposed utilitarian product for functional applications or as a concealed system with vegetation such as grass or native ground cover installed over the concrete. This system allows you to mitigate drainage issues while maintaining strong structural integrity that allows for some of the heaviest vehicles to operate unencumbered. The first application technique incorporates a reusable tool that creates the voids by having concrete placed in and around the tool formers prior to being pulled from the concrete slab. The second technique is using a single-use former that is placed on the sub grade with the concrete placed over the formers and the voids opened after the concrete hardens. The single-use formers are available in an ABS plastic former and the newly developed bio-degradable former, know as the Molded Pulp Former, that is made with post consumer recycled components. Grasscrete offers the ability to provide year-round access for a variety of applications requiring structural paving surfaces without compromising the aesthetics of the exterior landscaping. Grasscrete is a very sustainable product that can employ a large recycled material content both in the form of aggregate and binder such as fly ash or slag—its lifespan is indefinite and can be recycled itself to form the aggregates for future Grasscrete applications; providing Specifiers with a truly sustainable, eco-friendly system to accommodate a variety of needs. GREEN BENEFITS

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The benefit to Grasscrete for businesses and developers is that it drains at about the same rate as would an ordinary lawn in the same location. The presence of concrete has little effect on the drainage; the soil and the slope are the controlling factors which makes it beneficial for erosion control as well. Grasscrete is installed over a sub-base of gravel at a depth determined by the load bearing capacity required for the project. On site re-cycled fill materials are used in the sub-bases together with the use of topsoil in paving and retaining wall systems: as this is often available surplus from the excavation work it helps to avoid the unnecessary off-site disposal of waste materials. Grasscrete can also be installed over native soils saving money on excavation and gravel. The subsurface all depends on the needs and the water runoff requirements, from thick beds of stone to water piping systems. Grasscrete, as with many other "green" products generally costs 30% higher than traditional concrete pavement. At times however, using Grasscrete can eliminate or minimize the need for storm water collection systems which may in turn lead to substantial savings. Contrary to convention, the structural advantages that Grasscrete offers over pre-cast can make significant savings in both the "construction" and "lifetime" costs of a project. Sub-base depths are reduced and curb edge restraints can often be eliminated. The construction process is much faster than for precast and the forms can be delivered by the truckload to cover 7200 sq m which is the equivalent to fifty truckloads of pre-cast. This is a serious statistic that saves both money and polluted transportation waste. SUDS, better known as "Sustainable Urban Drainage" is becoming an increasingly used term with planners and developers seeking to mitigate the implications of handling surface water run-off on the local storm water network. Pre-formed tank water management often involves the use of self-draining paving layers together with the installation of pre-formed sub-ground

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retention tanks, to store surface water for a controlled release into the drainage network. Grasscrete provides a more uniform percolation process that creates a more natural balance thereby reducing the risk of shrinkage in clay soils due to the urbanized modification of water tables. Some other benefits of the Bomanite Grasscrete System, include the improved reflectance of the crete as compared to blacktop, reducing the heat island effect. Grasscrete handles runoff and storm drainage via river training, slope protection and channels. It is also a sound product for retaining pond bottoms thanks to its pervious nature and helps provide a food source and cover for pond inhabitants.

For lawned areas, the mesh is simply rolled out over the close-cropped turf, with adjacent rolls overlapping by 150-300mm, and anchored with ground pegs. Any dips, hollows, softspots etc, should be levelled out with grit sand or top soil before placing the mesh. Once laid, they can be left in-situ for the season, or even permanently, as most commercial mowers will ride over the embedded mesh without hindrance. For areas with longer grass, the meshes are placed after a mowing, and the grass is allowed to grow up and through the mesh, hiding it from view, yet providing sufficient stability to permit trafficking.

Sedge image by Photo by Nature Snooper /flickr.com

Overview Sedges compose over 1,000 species of the family Cyperaceae. They can be distinguished from grasses by their triangular-shaped stems. Sedges are found worldwide in wet areas, mostly in temperate and cold regions. Sedges make an appealing ground cover in wet, poorly drained areas, and are enjoying a surge in popularity as a lawn cover or landscape plant in home gardens. Use sedge for erosion control and soil stabilization in wet areas around ponds, in marshes and wetlands and in clumps as an ornamental plant.

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Step 1 Choose a site for your sedge. A damp location with full sun is best, but sedge will tolerate partial shade.

Step 2 Remove old lawn coverings and weeds. Kill existing vegetation in the area by repeated tilling, sodcutting, covering it with black plastic, or apply herbicide. Allow 2 or 3 weeks to be sure all vegetation in the planting site has died and newly sprouting weeds are eliminated.

Step 3 Add compost to loosen heavy soil. Fertilizer is not required unless the soil is extremely poor.

Step 4 Rake the site to smooth out the area and break up the soil.

Step 5 Sow sedge seeds over the area and press them lightly into the soil. Water the area heavily, until the soil is muddy.

Step 6 Mulch the area with sterile straw and maintain the moisture until the seeds sprout, approximately 1 to 2 weeks. Seed germination is not reliable and many gardeners prefer planting plugs or wild transplants.

Step 7 Plant sedge plugs approximately 6 to 8 inches apart. Keep the soil wet until the plants are established.

Step 8 Water sedge as needed to keep them moist. Sedge prefers wet roots, but can survive periods of drought.

Step 9 Remove weeds daily. Sedges have triangular shaped stems; remove grasses with rounded leaves and broad leaf weeds that may sprout. Pull weeds by hand to avoid disturbing the roots of your newly planted sedges.

Step 10 Trim the sedge monthly to a height of about 1 foot with a string trimmer during the growing season of the first year. Trimming the sedge encourages the roots to spread. Leave the sedge untrimmed at the end of the summer to protect the plants over the winter.

Step 11 Control sedges in the home landscape by placing a plastic root barrier to contain them. Sedges spread rapidly and can be invasive. Dig a trench around the desired containment area, at least a foot away from the roots. Place a plastic root barrier in the trench and refill the trench. The barrier will keep the sedge in the desired area.

Read more: How to Grow Sedge | Garden Guides http://www.gardenguides.com/70242-growsedge.html#ixzz2E6OKKMf0