SIDDHARTH GROUP OF INSTITUTIONS :: PUTTUR Siddharth Nagar, Narayanavanam Road 517583 QUESTION BANK (DESCRIPTIVE) Subject with Code : Geotechnical Engineering - II (16CE127) Year & Sem: III-B.Tech & II-Sem Course & Branch: B.Tech CE Regulation: R16 UNIT-I SOIL EXPLORATION 1. What is site investigation? What are the objectives of site investigation? [10 M] 2. What is soil exploration? What is the purpose of soil exploration? Explain how the sub-soil exploration is conducted? [10 M] 3. (a) What are different types of soil samples considered for soil testing? [5 M] (b) Discuss the salient points of auger boring with a neat sketch. [5 M] 4. With a neat sketch explain the process of advancing wash boring. What are the limitations of wash boring? [10 M] 5. Write short notes on the following: [10 M] a. Rotary drilling b. Percussion drilling c. Core drilling 6. (a) Describe the construct of spilt spoon sampler. [5 M] (b) Explain how the sample is extracted using split spoon sampler. [5 M] 7. The neat sketches explain how the soil samplers are extracted using scraper bucket and shellby tube sampler. [10 M] 8. (a) Explain in how the N-value is determined by conducting Standard Penetration Test? [5 M] (b) What are the corrections applied on N-value [5 M] 9. (a) Explain briefly how Cone Penetration Test is conducted in the field. [5 M] (b) List the necessary information to be furnished in a good soil report. [5 M] 10. The observed SPT value of a dense soil deposit which is 20 m below the ground water table is 48. The overburden soil is having unit of 17.5 kn/m 2. What is the corrected N-Value? [10 M] Geotechnical Engineering - II Page 1
UNIT-II EARTH SLOPE STABILITY 1. Discuss the method for checking the stability of an infinite slope in both cohesive and noncohesive soils. [10 M] 2. (a) What are different types of slope failures? Explain. [5 M] (b) A long natural slope of cohesionless soil is inclined at 12 o to the horizontal. Taking Φ = 30 o, determine the factor of safety of the slope. If the slope is completely submerged, what will be change in the factor of safety? [5 M] 3. How a slope is analysed using Swedish circle method? Derive an expression for the factor of safety. [10 M] 4. Describe Bishop s simplified method. Derive an expression for the factor of safety[10 M] 5. Discuss the friction circle method for the stability analysis of slopes? Can this method be used for purely cohesive soils? [10 M] 6. What is stability number? What is its utility in the analysis of stability of slopes? Discuss the uses of stability charts. [10 M] 7. A new canal is excavated to a depth of 5 m below ground level, through a soil having the following characteristics: c = 14 kn/m 3 ; Φ = 15 o ; e = 0.8 and G = 2.70. The slope of banks is 1 in 1. Calculate the factor of safety with respect to cohesion when the canal runs full. If it is suddenly and completely emptied, what will be the factor of safety? [10 M] 8. An embankment is inclined at an angle of 35 o and its height is 15 m. The angle of shearing resistance is 15 o and the cohesion intercept is 200 kn/m 2. The unit weight of soil is 18 kn/m 3. If Taylor s stability umber is 0.06, find the factor of safety with respect to cohesion. [10 M] 9. An earth dam of height 20 m is constructed of soil of which the properties are: γ = 20 kn/m 3 ; Φ = 20 o and c = 45 kn/m 2. The side slopes are inclined at 30 o to the horizontal. Find the factor of safety immediately after drawdown. [10 M] 10. A cutting is to be made in a soil with slope of 30 o to the horizontal and a depth of 15 m. the propertied of soil are: γ = 20 kn/m 3 ; Φ = 15 o and c = 25 kn/m 2. Determine the factor of safety of the slope against slip, assuming friction and cohesion to be mobilised to the same proportion of their ultimate values. [10 M] Geotechnical Engineering - II Page 2
UNIT III EARTH PRESSURE ON RETAINING WALLS 1. (a) What are different types of earth pressure? Give examples. [5 M] (b) A retaining wall, 6 m high, retains dry sand with an angle of friction of 30 o and unit weight of 1.62 g/cm 3. Determine the earth pressure at rest. [5 M] 2. (a) Define earth pressure at rest. Show the earth pressure distribution on a retaining wall, assuming the soil is dry. [5 M] (b) List and explain the stability considerations of a gravity retaining wall. [5 M] 3. What are the assumptions of Rankine s theory? Derive the expression for active pressure and passive pressure. [10 M] 4. What are the assumptions in Coulomb s theory? Compare Rankine s theory and Coulomb s theory. [10 M] 5. What are the limiting values of the lateral earth pressure at a depth of 3 m in a uniform sand fill with a unit weight of 20 kn/m 3 and a friction angle of 35 o? The ground surface is level. [10 M] 6. A gravity retaining wall retains 12 m of a backfill, γ = 17.7 kn/m 3, Φ = 25 o with a uniform horizontal surface. Assume the wall interfaces to be vertical, determine the magnitude and point of application of the total active pressure. If the water table is at a height of 6 m, how far do the magnitude and the point of application of active pressure changed? [10 M] 7. A wall 5.4 m high, retains sand. If the loose state the sand has a void ratio of 0.63 and Φ = 27 o, while the sense state, the corresponding values of void ratio and Φ are 0.36 and 45 o respectively. Compare the ratio of active and passive earth pressure in the two cases, assuming G = 2.64. [10 M] 8. A smooth backed vertical wall is 6.3 m high and retains a soil with a bulk unit weight of 18 kn/m 3 and Φ = 18 o. the top of the soil is level with the top of the wall and is horizontal. If the soil suface carries a uniformly distributed load of 4.5 kn/m 2, determine the total active thrust on the wall per linear metre of the wall and its point of application. [10 M] 9. A vertical retaining wall 10 m high supports a cohesionless fill with γ = 1.8 g/cm 3. The upper surface of the fill raises from the crest of the wall at tan angle of 20 o with the horizontal. Assuming Φ = 30 o and δ = 20 o, determine the total active earth pressure using the analytical approach of Coulomb. [10 M] 10. A retaining wall 3.6 m high, supports a dry chonesionless backfill with a plane ground surface sloping up wards at a surcharge angle of 10 o from the top of the wall. The back of the wall in inclined to the vertical at a positive better angle of 9 o. The unit weight of the backfill is 1.89 Geotechnical Engineering - II Page 3
t/m 3 and Φ = 30 o. Assuming wall friction angle of 12 o, determine the total active thrust by Rebhamn s method. [10 M] UNIT IV BEARING CAPACITY & SETTLEMENT 1. Define the following: [10 M] a. Ultimate bearing capacity b. Net ultimate bearing capacity c. Net safe bearing capacity d. Net safe settlement pressure e. Net allowable bearing pressure 2. Clearly state the assumptions made by Terzaghi and derive the bearing capacity equation for strip footing. [10 M] 3. (a) With neat sketches explain different types of shear failures. [5 M] (b) Determine the ultimate bearing capacity of a strip footing, 1.20 m wide, and having the depth of foundation of 1.0 m. use Terzaghi s theory and assume general shear failure. Take Φ = 35 o, γ = 18 kn/m 3, and C = 15 kn/m 2. [5 M] 4. What are different types of shallow foundations? Explain with the help of neat sketches. [10 M] 5. What are the points to be considered while fixing the depth of footing? Discuss Rankine s formula for the minimum depth. [10 M] 6. Describe how the plate load test is conducted with a neat sketch? What are its limitations and uses? [10 M] 7. Calculate the ultimate bearing capacity per unit area of a. a strip footing 1 m wide b. a square footing 3 m x 3 m, and c. a circular footing of 3 m diameter Where unit weight of the soil 1.8 t/m 3, cohesion = 2 t/m 2, Φ = 20 o, N C = 17.5, N q = 7.5 and Nγ = 5. [10 M] 8. A foundation in a sand will be 5 m wide and 1.5 m deep. Adopting a factor of safety of 2.5 what will be safe bearing capacity if the unit weight of the sand is 1.9 g/cm 3 and angle of internal friction is 35 o. How does it compare with safe loading capacity for surface loading? Consider N C = 57, N q = 44 and Nγ = 42. [10 M] 9. A footing 2 m square is laid at ta depth of 1.3 m below the ground surface. Determine the net ultimate bearing capacity suing IS code method. Unit weight of soil is 20 kn/m 3, angle of Geotechnical Engineering - II Page 4
internal friction is 30 o and the soil is cohesionless. Also estimate the ultimate bearing capacity of the footing when water table raises to the ground surface. [10 M] 10. Plate load tests were conducted in a c-φ soil, on plates of two different sizes and the following results were obtained: Load Size of plate Settlement 40 kn 0.3 m x 0.3 m 25 mm 100 kn 0.6 m x 0.6 m 25 mm Find the size of square footing to carry a load of 800 kn at the same specified settlement of 25 mm. [10 M] UNIT V PILE FOUNDATIONS 1. (a) What are the conditions where pile foundation is more suitable than a shallow foundation [5 M] (b) A square concrete pile of 30 cm side, 10 m long is driven into coarse sand (γ = 18.5 kn/m 3, N = 20). Determine the allowable load when a factor of safety is 3. [5 M] 2. Describe how the piles are classified based on transfer of load, method of construction and use. [10 M] 3. (a) How do you estimate group capacity of piles in sand? [5 M] (b) A pile is driven with a single acting steam hammer of weight 15 kn with a free fall of 900 mm. the final set, the average of the last three blows, is 27.5 mm. Fid the safe load using the Engineering News Formula. [5 M] 4. With a neat sketch how pile load test is conducted and draw a typical load-settlement curve for loading during this test. [10 M] 5. (a) What is the effect of negative friction on pile? [5 M] (b) In a 16 pile group, the pile diameter is 45 cm and centre to centre spacing of the square group is 1.5 m. If c = 50 kn/m 2, determine whether the failure would occur with the pile acting individually, or as a group? Neglect bearing at the tipe of the pile. All piles are 10 m long. Take m = 0.7 for shear mobilisation around each pile. [5 M] 6. (a) Discuss how ultimate load is given by Engineering News Record Formula. [5 M] (b) A 30 cm diameter concrete pile is driven into a homogeneous consolidated clay deposit (C u = 40 kn/m 2, α = 0.7). If the embedded length is 10 m, estimate the safe load if factor of safety is 2.5. [5 M] Geotechnical Engineering - II Page 5
7. A square group of 9 piles was driven into soft clay extending to a large depth. The diameter and length of the piles were 30 cm and 9 m respectively. If the unconfined compression strength of the clay is 9 t/m 2, and the pile spacing is 90 cm centre to centre, what is the capacity of the group? Assume a factor of safety of 2.5 and adhesion factor of 0.75. [10 M] 8. A precast concrete pile is driven with a 50 kn hammer, having a free fall of 1.0 m. If the penetration in the last blow is 0.5 cm, determine the load carrying capacity of the pile using Engineering News Record formula. Consider a factor of safety of 6.0. [10 M] 9. (a) With a neat sketch explain how ultimate failure load of a pile is estimated using static method. [5 M] (b) How do you estimate group capacity of piles in clay? [5 M] 10. A group of friction piles of 30 cm diameter is subjected to a net load of 2000 kn, as shown in figure. Estimate the consolidation settlement. [10 M] Figure Prepared by: M. Prem Kumar & C. Siva Kumar Prasad Geotechnical Engineering - II Page 6