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VTU Civil Engineering (Semester 6)
Geotechnical Engineering 2
June 2015
Total marks: --
Total time: --
INSTRUCTIONS
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary

1 (a) Explain the wash boring method, with the help of a neat sketch.
8 M
1 (b) With a neat sketch, explain the seismic refraction method.
6 M
1 (c) Establish the location of ground water in a clayey strata, water in bore was bailed out to a depth of 10.67m below ground surface and rise of water recorded at 24 hour interval. h1=64.0cm, h1=64.0cm, h2=57.9cm and h3=51.8cm.
6 M

2 (a) Derive an expression for vertical pressure under a uniformly loaded circular area along vertical symmetrical axis.
10 M
2 (b) Define isobar. Construct an isobar for a vertical stress of 40 kN/m2 when ground surface is subjected to a concentrated load of 1000kN.
10 M

3 (a) What are the assumptions made in deriving Laplace equation?
4 M
3 (b) Describe the Casagrande's method to locate the phreatic line in a homogeneous earth dam with a horizontal filter at its toe.
10 M
3 (c) A 3m thick soil stratum has coefficient of permeability of 3×10-7m/sec. A separate test gave porosity of 40% and bulk unit weight of 21 kN/m3 at a water content of 31%, Determine the head at which upward seepage will cause quick sand condition. What is the flow required to maintain critical condition?
6 M

4 (a) Compare Rankine's and Coulomb's theory of earth pressure.
4 M
4 (b) Explain how do you determine Active Earth pressure by Rebhann's method.
10 M
4 (c) A retaining wall, 6m high, retains dry sand with an angle of friction of 30° and unit weight of 16.2 kN/m3. Determine the earth pressure at rest. If the water table rises to the top of the wall, determine the increase in the thrust on the wall. Assume the submerged unit weight of sand is 10 kN/m3.
6 M

5 (a) Explain the causes for a slope failure and list the types of slope failures.
6 M
5 (b) Explain Swedish method of slices of stability analysis of slopes.
6 M
5 (c) A 5m deep canal has side slopes of 1:1. The properties of soil are Cu=20 kN/m2, ϕu=10°. e=0.8 and G=2.8. If Taylor's stability number is 0.108. Determine the factor of safety with respect to cohesion when the canal runs full. Also find the same in case of sudden drawdown, if Taylor's stability number for this condition is 0.137.
8 M

6 (a) List the assumptions made in Terzaghi analysis.
4 M
6 (b) Discuss the effect of ground water table on bearing capacity of soils.
6 M
6 (c) A strip footing 2m wide carries a load intensity of 400kN/m2 at a depth of 1.2m is sand. The rsat of sand is 19.5 kN/m3 and unit weight above water table is 16.8 kN/m3, ϕ=35°, using Targahi's analysis determine factor of safety with respect to shear failure for the following locations of water table. Take Nq=41.4, N=42.4.
i) Water table 4m below ground level
ii) Water table 1.2m below ground level.
10 M

7 (a) What are the different types of settlement of footings? Explain.
8 M
7 (b) Determine the elastic settlement of footing 3m×3m resting on a sandy soil. Given Es=45000 kN/m2 and μ=0.3, Footing carries a load of 2000 KN. Take Iw=0.82.
6 M
7 (c) A normally consolidated clay layer is 18m thick. Natural water content is 45%, saturated unit weight is 18kN/m3, specific gravity is 2.7 and liquid limit is 63%. The vertical stress increment at the centre of clay layer due to foundation load is 9kN/m2. Determine the settlement.
6 M

8 (a) Explain the factors influencing the selection of depth of foundation.
6 M
8 (b) Discuss the proportioning of combined Trapezoidal footings.
8 M
8 (c) Explain determination of the pile load capacity in detail.
6 M

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