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- 1. Subject Code CED1122 R12 VNR VIGNANA JYOTHI INSTITUTE OF ENGINEERING AND TECHNOLOGY (AUTONOMOUS) B.Tech. III Year II Semester Adv. Supplementary Examinations, June/July, 2015 GEOTECHNICAL ENGINEERING-II (CE) Time: 3Hours Max. Marks: 70M PART-A (Answer ALL Questions) 1. Answer in one sentence 5X1=5M a) In a Standard Penetration Test, the number of blows for the first 15 cm penetration, second 15 cm penetration and the last 15 cm penetration is 9, 14 and 16 respectively. Find the observed N-value. b) Find the factor of safety of an infinite slope having a slope angle of 280 . The slope consists of cohesionless soil with angle of internal friction of 310 . c) When movement of a wall under the earth pressure from a sandy backfill was prevented, the lateral earth pressure was half of the vertical pressure at a point. Find the angle of internal friction of the backfill. d) Name the IS code dealing with the permissible settlement. e) As per Engineering News formula, what is the ratio of loss of energy in driving energy in the case of drop hammer to that of steam hammer? 2. Answer the following in two sentence each 5X2= 10M a) In a rock core drilling, the sum of lengths of rock pieces having length more than 100 mm is 750 mm. If the length of run is 1 m, find RQD. b) A temporary trench with vertical sides is to be excavated in a purely cohesive soil with unit weight of 19 kN/m3 and cohesion of 25 kPa. Determine the initial depth upto which the trench can be excavated without any lateral support. Taylor’s stability number for this case is equal to 0.261. c) Say true or false and justify your answer: The greater the depth of tension cracks, the greater is the cohesion of clayey soil d) If the gross ultimate bearing capacity of a foundation is 300 kPa, the unit weight of the soil is 20 kN/m3 and the depth of the foundation is 1.5 m, find the gross safe bearing capacity adopting a factor of safety of 3. e) Can you apply dynamic formulae to piles driven in loose saturated sand? Justify your answer. 3. Answer the following in brief 5X3=15M a) Enumerate the topics that must be included in a soil investigation report. b) A 15-m high embankment is inclined at 300 to the horizontal. If angle of internal friction and cohesion are respectively 150 and 15 kPa, find the factor of safety with respect to cohesion. The unit weight of the soil is 17.5 kN/m3 . Assume the slope to be infinite. c) State the assumptions made in Coulomb’s earth pressure theory. d) Distinguish between immediate and consolidation settlement. e) What is meant by ‘Negative skin friction’? What are the situations where this is developed? Page 1 of 3
- 2. PART – B Answer any FOUR Questions 4X10=40M 4. a) The inner diameters of sampling tube and that of cutting edge of a sampler are 70 mm and 68 mm respectively, their outer diameters are respectively 72 mm and 74 mm. Determine the inside clearance, outside clearance and area ratio of the sampler. Comment on the suitability of the sampler for collecting undisturbed sample. 7M b) Discuss the limitations of the static cone penetration test 3M 5. An embankment 10-m high is inclined at angle of 400 to the horizontal. A slip circle method analysis gives the following forces per running metre. ∑ Shearing forces = 450 kN ∑ Normal forces = 873.2 kN ∑ Neutral forces = 218.2 kN The length of the failure arc is 22.0 m. Soil tests in the laboratory indicate that angle of internal friction is 150 and cohesion is 20 kPa. Find the factor of safety with respect to i. Shear strength ii. Cohesion. 6. A retaining wall, 4.5 m high retains soil with cohesion of 20 kPa, angle of internal friction of 300 and unit weight of 20 kN/m3 , with horizontal surface level with the top of the wall. The backfill carries a surcharge of 30 kPa. Compute the total active thrust on the wall and its point of application. Use Rankine’s theory for solving the problem and state the assumptions made in the theory. 7. Following are the results of plate load test conducted on a 600-mm square plate at a depth of 2 m below the ground surface on a sandy soil which extends upto a large depth. Determine the available factor of safety against shear failure and settlement of footing of size 3 m x 3 m carrying a load of 1100 kN located at a depth of 2 m from the ground surface. Load Intensity, kPa 0 50 100 150 200 250 300 350 400 Settlement, mm 0 1.0 2.0 3.75 5.5 8.15 11.75 17.0 22.5 8. A footing 1.5 m x 1.5 m is placed at a depth of 1.8 m in stratum of saturated clay extending upto a depth of 5 m from the ground level. The unconfined compressive strength, submerged unit weight, liquid limit, and specific gravity of solids of the clay are 110 kPa, 9 kN/m3 , 40%, and 2.65 respectively. Determine the allowable bearing capacity for the footing if the factor of safety against shear failure is not to be less than 3 and consolidation settlement is not to be more than 75 mm. The ground water table is quite close to the ground level. Page 2 of 3
- 3. 9. A 4-pile group arranged in a square pattern with c/c spacing of 1.0 m is used as a foundation for a column carrying a load of 800 kN. The piles of length 15m and diameter 300mm are driven in sandy soil of unit weight of 19.81 kN/m3 and angle of internal friction of 360 . The ground water table is at the ground surface. The earth pressure coefficient and angle of wall friction can be taken as 1.5 and 270 respectively. Take Nq = 58 for φ = 360 . Find the available factor of safety against shear failure. Also, find the settlement of the pile group, if the results of pile load test conducted on a single pile are given below. Load, kN 0 100 200 300 400 500 600 Settlement, mm 0 1.0 2.5 6.0 8.0 15.0 35.0 ****** Page 3 of 3