Monday, November 28, 2011

Geotechnical Engineering II - Question Bank


LAB MANUAL

Geotechnical Engineering – II

Unit 5:

1. It is proposed to lay a suitable type of foundation at a depth of 1.50m below the GL on soil a c-Φ soil with c=30 Kpa and Φ=25°, γ=17.50 kN/cum. Given Nc’=14.80; Nq’=5.60; Nγ’=3.20. Estimate the ultimate bearing capacity of a (i) 2m wide strip footing, (ii) 2m wide square footing, (iii) 2m wide circular footing. Comment on the results.

2. A 2m wide square footing is laid at a depth of 1.20 m below the GL on a c-Φ soil with c=40 Kpa and Φ=20°, γ=17 kN/cum. Given Nc’=11.80; Nq’=3.90; Nγ’=1.70. Using Terazaghi’s theory, compute the ultimate bearing capacity when the GWT is
(i) 5m below GL (ii) 2m below GL (iii) at GL.
Assume the change in shear parameters due to saturation is negligible.

3. Explain the types of shear failures experienced by shallow foundations. Mention the parameters to decide type of shear failure.

4. A continuous footing of width 2.5m rests 1.5m below the ground surface in clay. The unconfined compressive strength of the clay is 150kN/m2. Calculate the ultimate bearing capacity of the footing. When there is no effect of water table and when water table reaches ground surface. Take γ=19kN/m3, γsat=20kN/m3

5. What is a strip footing? When it is preferred?

6. List out different types of foundations. State the circumstances to go for combined foundations

7. A continuous footing of width 2.5m rests 1.5m below the ground surface in clay. The unconfined compressive strength of the clay is 150kN/m2. Calculate the ultimate bearing capacity of the footing. When there is no effect of water table and when water table reaches ground surface. Take γ=19kN/m3, γsat=20kN/m3.

8 Define the following:
i) Net ultimate bearing capacity.
ii) Unit soil pressure.
iii) Allowable bearing capacity.

9. A square footing 1.8mx1.8m is placed over loose sand of bulk density 1.6g/cc, saturated density 1.82g/cc and at a depth of 0.8m. The angle of shearing resistance is 300. Determine the ultimate bearing capacity when there is no effect of water table and when it is submerged (for φ= 300, Nc=30.14, Nq=18.4 and Nγ=15.1).

10. Differentiate between Safe bearing Capacity and Allowable bearing capacity.


Unit 6:

1. Distinguish between immediate and consolidation settlements. What are the limits of maximum and differential settlements according to I.S. codes?

2. A raft foundation of size 20m X 30m exerts a uniform pressure of 180kN/m2 on sub soil. Determine the immediate settlement of soil by assuming E= 45Mn/m2 and poisons ratio 0.5.

3 Discuss the situations for adopting the SPT test for determining the bearing capacity.

4. Determine the allowable bearing capacity of a 1.5m X 1.5m square footing placed at a depth of 2.0m in a sandy deposit having a unit weight of 19kN/m3 with SPT value of 37. Water table is at depth of 1.5m. Determine the allowable bearing capacity for 50mm permissible settlement after applying suitable corrections for SPT value.


Unit 7:

1. A 300mm dia. Pre-cast RCC pile is driven in to a clay bed to a depth of 9m. The average properties of the clay along the shaft of pile include, c = 40 kPa; α = 0.74. However, the un-confined compressive strength of clay at tip of the pile was found to be 120 kPa. Estimate the safe load carrying capacity of the pile with a FOS of 3.

2. Explain the construction and use of “Under-reamed Pile foundations”.

3. A group of 20 piles, arranged in 4x5 pattern are provided in a Clay deposit to a depth of 12m.The size of each pile is 600mm dia provided at a c/c spacing of 1.80m. The average properties of the clay are qu=160kPa, adhesion factor=0.58. Determine the safe load carrying capacity of the pile group. Adopt FS=2.50.

4. Give classification of piles.

5. A group of 15 piles of 450mm diameter each are arranged in 3 x 5 pattern to a depth of 9m in a 16m thick medium stiff clay. The average unconfined compressive strength of clay is found to be 120 kPa. The adhesion factor between concrete and in-situ clay is found to be 0.58. Estimate the safe load carrying capacity of the pile group with an overall factor of safety of 3.0, if the center to center spacing of piles is 0.9m

6. Write a note on “Dynamic formulae” and comment on their validity

7. A R.C.C. pile of size 30cm X 30cm and 10m long is driven into coarse sand with unit weight of 16kN/m3 and angle of internal friction of 310. What is the allowable load on the pile? For φ=310, N q= 16 and N γ = 14.Take K=1.0 and factor of safety of 3.0.

8. What is negative skin friction in piles? Explain.

9. Sketch an open well foundation and show the various components. Explain the functions of various components

10. Explain the “Pile Load Tests” in detail


Unit 8:

1. Describe various types of Caisson Foundations and comment on their suitability.

2 Explain in detail the procedure of “Sinking of Well foundations”.

3. With the help of a neat sketch, show the components of an “Open Caisson” and explain the function of each component.

4. With the help of neat sketch, show the components of a “Pneumatic Caisson” and explain their function. Also explain the procedure of sinking of “Pneumatic Caissons”.


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