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CENG 6207 Advanced Soil Mechanics

ADDIS ABABA SCIENCE AND TECHNOLOGY UNIVERSITY COLLAGE OF ARICTURE AND CIVIL ENGINEERING GEOTECHNICAL ENGINEERING SPECILIZATION Date: November 27, 2016 Time: 2:30Hr

Advanced Soil Mechanics CENG 6207 Year 2015/2016

FINAL EXAM Note: 1. Solve all problems 2. No credit for incorrect answers 3. The examination is closed book but two page formulas are allowed.

1. A 5-m-thick clay layer, drained at the top only, has some sand drains. A uniform surcharge is applied at the top of the clay layer. Calculate the average degree of consolidation for combined vertical and radial drainage after 100 days of load application, given Cvr = Cv= 4mm2/ min, de = 2m, and rw = 0.2m. 2. Figure 1 represents a steady state one dimensional seepage situation in which the upstream and downstream water levels are maintained constant. The container in which the soil (permeability k = 1.2 x 10-5 m/sec, and porosity n = 0.2) has been placed consists of two sections having different diameters. The areas of the upper (AU) and lower (AL) sections are 28cm2 and 14cm2 respectively. (a) Determine the rate of seepage flow through the soil. (b) Calculate the actual velocity of flow through the upper section of soil. (c) Plot the total head, pressure head and elevation head along the tube. (Hint: Firstly it is necessary to establish an arbitrary datum from which the elevation head may be measured. Let this datum be located a distance of 4cm below the lower boundary of the soil.)

Figuer.1

3. In a material with a Poisson ratio of μ= 0.33, how much stiffer is the material if its sides are constrained (not allowed to move in or out)?

Argaw Asha (PhD)

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CENG 6207 Advanced Soil Mechanics

4. Two identical samples of clay are isotropically normally compressed to an all-round effective pressure of 200 kPa and are then allowed to swell back to an effective isotropic pressure of 100 kPa.The first sample is then subjected to a standard drained compression test. What is the deviator stress at failure and what is the volumetric strain experienced by the sample at failure? The second sample is subjected to a standard undrained compression test. What are the deviator stress and pore pressure at failure, if there is initially a back pressure of 100 kPa? Assume that the soil has the following critical state properties:

= 0.95, = 0.094, = 0.036, = 2.06 and = 2.12 5. Derive the relationship for bulk modulus (B): B=E/3(1-μ), Show all necessary steps and assumptions. 6. Triaxial test data for the soil sample collected from Ayer Tena area given below in Table 1. The cell pressure (c)=300kPa and it was zero before application. The initial height of the sample (Lo)=100cm ∆L ( 0 2.5 5 7.5 10 15 20 change in height,cm) 300 500 720 920 1050 1200 1250 ( ) 1

U

120

150

150

120

80

10

-60

Estimate a. The value of B (skempton pore pressure parameter) state where the sample is saturated or not b. Plot deviator Stress vs Strain c. Plot ‘A” vs Strain 7. Explain in detail stress path for normally consolidated undrained and drained soil (use sketch)

Argaw Asha (PhD)

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