Jawahar Nehru Technical University JNTU
B.Tech I Semester Examinations,
Civil Engineering Dec-2011
ADVANCED FOUNDATION ENGINEERING
Time: 3 hours Max Marks: 80Answer any FIVE Questions,All Questions carry equal marks ? ? ? ? ?
Q.1. (a) Circular caisson has an inside diameter of 3m. How thick must the wall be to overcome a skin friction of 20 KPa if it is 14 m long and of concrete (= 23.5 kN/m3) using its self weight for sinking?
(b) Differentiate drilled pier and caisson. What are the conditions in which a drilled pier is more suitable than a caisson? [8+8]
Q.2. (a) Explain the Reese and Matlock's approach for laterally loaded piles analysis.
(b) A 200 mm diameter, 5 m long piles are used as foundations for a column carrying 500 kN in a uniform deposit of normally consolidated clay having sat = 19 kN/m3, liquid limit 40%, void ratio 1.05. There are nine piles in the group arranged in a square pattern with centre to center spacing 500 mm. Hard stratum exists at a depth of 7 m. Estimate the settlement of a pile group. [8+8]
3. A wall 15 m high has to be designed so as to retain dry sand. Under loose condition the sand has a void ratio of 0.65 and of 320, and under dense condition the void ratio and 0 are 0.41 and 430 respectively, and G = 2.65. Compute the resultant lateral pressures for active and passive cases for both the density conditions. Recommend a suitable resultant lateral force if the wall has to be designed for:
(a) The active case
(b) The passive case. [16]
Q.4. (a) What is negative skin friction? How it is estimated in a soil consisting of loose back ll.
(b) Compute the safe carrying capacity of a 500 mm diameter and 12.5 m long concrete pile driven into a granular soil by a diesel hammer with a 30 kN ram and 900 mm stroke. The set is observed to be 12 mm per blow and the total elastic compression is 25 mm.The hammer effciency is 85% and the coefficient of restitution is 0.5. Allow a factor of safety of 3.0. Use Hiley's formula. [8+8]
Q.5. (a) Write short notes on stability of the bottom of cut in sand.
(b) Write a brief note on sheet pile wall with respect to failure mechanism. [16]
Q.6. Write in detail about design of foundations on expansive soils. [16]
Q.7.A rectangular footing of size 3 6 m is founded at a depth of 2 m in medium dense sand of angle of friction = 360. The soil is submerged up to base level and is saturated above. The saturated unit weight of sand is 18 kN/m3. By the method of Hansen's determine the ultimate bearing capacity for the following cases:
(a) The loading is vertical and acts at an eccentricity of 0.5m in both the direction of the footing,
(b) The loading is symmetrical but inclined at an angle of 200 to the vertical parallel to the shorter side. [16]
Q.8. (a) What is the meaning of the following terms: uniform settlement,differential settlement, angular distortion, tilt.
(b) A rectangular footing of dimension 4m 2m is founded at a depth of 2 m on a soil having E = 48 MN/m2 and = 0.50. The soil is underlain by a rigid layer at a depth of 10 m from the ground surface. The foundation transmits a uniform contact pressure of 200 kN/m2. Estimate the average immediate settlement likely to occur. [6+10]
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