Geotechnical Engineering - II (Question Bank)

Geotechnical Engineering – II

Unit 1:

1. a) Differentiate un-disturbed and disturbed soil samples.

b) Explain in detail the test set up and procedure of plate load test as per IS: 1885 including the analysis of data and its limitations.

2. a) Explain Objective and various methods of soil exploration and comment on suitability of each of them.

b) Write a detailed note on the test set up and procedure of Standard Penetration Test including the corrections to be applied.

3. a) Explain the “Log of Bore Hole” details.

. b) Explain the method of collection of sample in Cohesion-less soils including the description of the sampler used.

4 a) Explain in detail the test set up and procedure of “Pressure Meter Test” including the analysis of data and its suitability.

b) Describe the factors governing depth of investigation.

Unit 2:

1. a) Compare the “Swedish Slip Circle method” with “Method of slices”.

b) An excavation has to be made with an inclination of 40° in a soil with c’=40 kPa, Φ’=10° and γ=18 kN/cum. What is the maximum height of the slope with a factor of safety of 2.01. The Taylor’s stability number for the above conditions is given as 0.097.

2. a) Discuss various types of failure of slopes and explain the necessary conditions for each of them to occur.

b) Explain the method of slices for estimation of factor of safety of finite slopes. Also, obtain the expression for factor of safety of a c- Φ slope.

3 a) A long natural slope in an over consolidated Clay (c1 = 10 kN/m2, φ=250, γsat= 20 kN/m3) is inclined at 100 to the horizontal. The water table is at the surface and the seepage is parallel to the slope. If a plane slip had developed at a depth of 5m below the surface, determine the factor of safety. Take γw= 10 kN/m3

b) Describe the stability of slope of an earthen dam in “sudden draw down” conditions.

4. a) Derive an expression for the factor of safety of infinite slope in submerged cohesion less soils.

b) An embankment is constructed at an angle of 600 to the horizontal. The cohesive strength of the embankment material is 40 kN/m2 and the angle of shearing resistance is 0. Its unit weight is 18 kN/m3. Calculate the safe height of the embankment for a factor of safety of 1.5. Assume the stability number as 0.91.

Unit 3:

1. a) Explain the earth pressure in active, passive and at rest conditions.

b) A 9m high retaining wall is supporting a back fill consisting of two types of soils. The water table is located at a depth of 5m below the top. The properties of soil from 0 to 3m include c = 0 kN/sqm; Φ = 330; γ = 17 kN/cum and those for soil from 3m to 9m include c = 0 kN/sqm; Φ = 400; γ = 18.50 kN/cum, γ sub = 20.50 kN/cum. Plot the distribution of active and passive earth pressure and determine the magnitude and point of application of total active and passive earth pressure acting on the retaining wall.

2. a) Compare the Rankine’s and Coulomb’s theories for computation of earth pressure, critically and suggest the suitability of these methods.

b) A 8m high retaining wall is supporting a c-Φ backfill having c=40 kN/sqm ; Φ=24° ; γ=18.50 kN/cum. Plot the distribution of active and passive earth pressure and determine the magnitude and point of application of total active and passive earth pressure acting on the retaining wall.

3. a) A 10m high retaining wall is supporting a back fill consisting of two types of soils. The water table is located at a depth of 6m below the top. The properties of soil from 0 to 4m include c=30 kN/sqm ; Φ=30° ; γ=17 kN/cum and those for soil from 4m to 10m include c=10 kN/sqm ; Φ=40° ; γ=18.50 kN/cum, γsat =20.50 kN/cum. Plot the distribution of active earth pressure and determine the magnitude and point of application of total active earth pressure acting on the retaining wall.

b) Explain the procedure of Culmann’s graphical method for computation of earth pressure

4. a) Explain the procedure for computation of active earth pressure in case of backfill with its top inclined to horizontal .

b) A 7m high retaining wall is supporting a back fill consisting of two types of soils.

The water table is located at a depth of 5m below the top. A capillary raise of 0.90m was found. The properties of soil from 0 to 3m include c=0 kN/sqm ; Φ=18° ; γ=16.50 kN/cum and those for soil from 3m to 7m include c=0 kN/sqm ; Φ=36° ; γ=18 kN/cum, γsub =20 kN/cum. A surcharge of 200 kPa is applied on the top of backfill. Plot the distribution of active earth pressure and determine the magnitude and point of application of total active earth pressure acting on the retaining wall.

Unit 4:

1. A trapezoidal gravity retaining wall of height 6m with top and bottom widths as 0.45m and 1.20m respectively is constructed in RCC with a unit weight of 25 kN/cum. Its bottom is resting 2m below the GL on soil having c = 0 kN/sqm; Φ = 360; γ = 18kN/cum; the friction angle is 2/3 of Φ. The allowable bearing capacity of the soil for this case is found to be 200 kN/sqm. The wall is supporting the 4m thick back fill above GL made of soil having c = 0 kN/sqm; Φ = 300 ; γ = 17.50 kN/cum. Analyse the stability of wall against overturning, sliding and bearing capacity.

2. Design a gravity retaining wall of height 3m with uniform thickness (ie. rectangular in cross section) constructed in RRM with a unit weight of 24 kN/cum. The average properties of soil from top to bottom of wall include c=0 kN/sqm ; Φ=36° ; γ=18kN/cum; the friction angle is 2/3 of Φ. The allowable bearing capacity of the soil for this case is found to be 200 kN/sqm. Analyse the stability of wall against overturning, sliding and bearing capacity.

b) Explain the significance of weep holes in performance of retaining walls

3. A gravity retaining wall of height 3m with uniform thickness (ie. rectangular in cross section) of 1.20m is constructed in RRM with a unit weight of 24 kN/cum. The average properties of soil from top to bottom of wall include c=0 kN/sqm ; Φ=30°. Subsequently, 1m high fill is placed on top of the existing backfill after constructing a 0.60m thick wall above the existing wall matching with the backfill side face of wall (ie., the offset is provided on the otherside of backfill) Analyse the stability of wall against overturning before and after raising the height of backfill.

4. An L–shaped retaining wall is constructed to retain dry sand. The unit weight of sand is 17kN/m3 and the angle of shearing resistance is 320.The base of the wall is placed 6.0m below the top of the backfill. The thickness of the base and that of the stem is 0.4m. The base width is 3.5m. Unit weight of masonry is given as 22kN/m3. The angle of friction between the concrete and the foundation material can be taken as 200 and Allowable bearing capacity as 220kN/m2. Check the stability of the retaining wall against overturning and maximum pressure.