Model Question Paper - 2

MODEL QUESTION PAPER - 2 GEOTECHNICAL ENGINEERING ETCE 210 1. Answer the following questions

a. Explain ZAV line and how this is plotted on compaction curve. 2

b. Plot failure envelop for a c- soil on the basis of Mohr-Coulomb failure hypothesis

c. What are the assumptions involved in Terzaghi’s one dimensional consolidation theory 5

d. Plot the phase diagram for partially saturated, saturated and dry soil 3

e. Derive expression for obtaining the specific gravity of soil particles using pycnometer method 5

f. List down the factors affecting the permeability of soil 3

g. Draw Plasticity chart as per BIS soil classification system 2

h. Differentiate dry unit weight of soil and unit weight of soil solids 2

i. What are the factors that affect the compaction characteristics of soil 2

UNIT – 1

2. A sandy soil in its loosest state has a void ratio of 0.92 and a void ratio of 0.53 in the densest state. At its natural state, its relative density is 65%. The specific gravity of solid particles is 2.65. Calculate the void ratio in its natural state as well as dry unit weight in the densest, loosest and natural state. 10

a. The bulk unit weight of a soil is 18.5 kN/m3 and the specific gravity of soil particles is 2.67. At the moisture content of 18%, calculate the void ratio and degree of saturation of the soil. 5 b. 500 m3 of embankment is to be constructed at a bulk density of 18 kN/m3 and moisture content of 16%. How many cubic meters of earth is to be excavated from a borrow are where the in situ density is 16 kN/m3 and water content is 20%. 5

3. A sample of inorganic soil has the following grain size characteristics.

Size (mm) % passing 2.0 mm 95% 0.075 mm 78%

The liquid limit and plastic limit of the soil is 65% and 32%, respectively. Classify the soil as per BIS soil classification system. 7.5

A pycnometer test was used to obtain the moisture content of the wet soil. The specific gravity of the soil solids was obtained as 2.67. Following observations were made in the pycnometer test: Weight of the moist soil = 240.63 gm Weight of pycnometer + soil + water = 3162.80 gm Weight of pycnometer + water = 2980 gm Calculate the moisture content of the soil. 7.5

4. A field density test was conducted using core cutter method and the following data were obtained. Weight of empty core cutter = 23.67 N Weight of soil + core cutter = 45.33 N Inside diameter of core cutter = 90 mm Height of core cutter = 180 mm

For moisture content determination Weight of wet soil sample = 0.48 gm Weight of oven dried soil sample = 0.37 gm Specific gravity of soil solids = 2.68 Determine the dry density, void ratio and degree of saturation of the soil. 7.5

OR An embankment is to be constructed with the following specification: Volume = 750 m3, bulk density = 17.4 kN/m3, water content = 18%. The soil is to be borrowed from a nearby area. The in situ field density test was conducted at the borrow site and the bulk density and moisture content were obtained as 16.5 kN/m3 and 16%, respectively. Calculate the amount of soil to be excavated from the borrow area and the amount of water to be added in the borrowed soil to complete the construction of embankment as per specifications. Assume specific gravity of soil particles Gs = 2.65 and unit weight of water = 9.81 kN/m3. 7.5

UNIT - II

5. In a flownet for a sheet pile wall, the number of flow paths is 7 and the number of equipotential drops is 15. Determine the seepage under the wall (in l/day) given the coefficient of permeability k = 2.54 × 10-3 mm/sec and head causing flow is 5.0 m. 5

A soil sample 95 mm high and 6000 mm2 in cross section was subjected to a falling head permeability test. The head fall from 500 mm to 300 mm occurred in 1500 seconds. The diameter of the stand pipe was 25 mm. Estimate the coefficient of permeability of the soil. 5

6. The effective size of the soil is 0.06 mm. assuming the average void ratio of the soil to be 0.2 times the effective size of the soil. Determine the capillary rise in the soil. 5

A foundation trench is to be excavated in a stratum of stiff clay, 10 m thick, underlain by a bed of coarse sand. In a trial borehole, the ground water was observed to rise to an elevation 3.5 m below ground surface. Determine the depth up to which an excavation can be safely carried out without the danger of the bottom becoming unstable under the artesian pressure in the sand stratum. The specific gravity of clay particle is 2.75 and void 3 ratio is 0.8. Unit weight of water (w) = 9.81 KN/m 5

7. A soil deposit consists of 4 layers of thickness 1.0m, 1.5m, 0.5m and 2.0 m with coefficient of permeability values k1 = 4 ×10-3 mm/sec, k2 = 1.0 ×10-3 mm/sec, k3 = 0.05 ×10-3 mm/sec and k4 = 45 ×10-3 mm/sec, respectively. Determine the ratio kH/kV. Also obtain the discharge in each layer when the flow is taking place in the horizontal direction under the hydraulic gradient value of 0.85.

What will be the head loss in each layer if the flow takes place in vertical direction under the same hydraulic gradient value? 15 OR

A stratum of clay 5 m deep has liquid limit value of 55%. The surface of the clay is at 7.5 m below the ground level. The natural moisture content of clay and specific gravity of soil particles are 35% and 2.65, respectively. The ground water level is 2 m below the ground surface. The clay layer is sandwiched between the sand layers. The sand layer above the ground water table is dry. The void ratio and Gs value of sand layer is 0.60 and 2.75, respectively. The sand below the GWT is saturated and the clay is normally consolidated. The weight of superstructure coming on the coming on the top of the sand increases the overburden pressure on clay by 75 kPa. Estimate the consolidation settlement of the clay. 15

UNIT – III

8. A proposed highway embankment will contain 8,50,000 m3 of earth. It is to be compacted as a void ratio of 0.63. The void ratio of the soil at the borrow pit is 0.85. the cost of excavating, hauling and compacting the soil is Rs 1500/- per 100 m3. What is the cost of construction? 10

Following results were obtained from compaction test:

Weight of mould + wet soil (N) 28.6 32.4 31.2 30.7 28.54 Water content (%) 10 12 14 16 18

Volume of the mould = 1000 cm3, weight of the mould = 10N and specific gravity of the soil = 2.65. (a) Plot the compaction curve showing OMC and MDD. (b) Plot ZAV line. (c) Determine the degree of saturation at MDD. 10

9. A specimen of sand tested in a direct shear test apparatus failed under a shear stress of 180 kPa, when the normal stress was 312 kPa. A triaxial test was conducted on the same sand at the same void ratio at a confining pressure of 100 kPa. What will be the deviator stress at failure? Use Mohr-Coulomb failure criterion 10

OR In an in situ vane shear test on saturated clay, a torque of 35 Nm was required to shear the soil. The diameter of the vane was 55 mm and length 105 mm. calculate the undrained shear strength of the clay. The vane was then rotated rapidly to cause re-moulding of the soil. The torque required to shear the soil in the remoulded state was 5 Nm. Determine the sensitivity of the clay. 10

10. Discuss the typical results obtained from UU, CU and CD tests performed on saturated clay soil sample. Use Mohr-Circle of stress and Mohr-Coulomb failure concept for explanation. 5

UNIT IV

11. The field N value in a deposit of fully submerged fine sand was 45 at a depth of 5.5 m. The average saturated unit weight of the soil is 19 kN/m3. Calculate the corrected N value as per BIS specifications. 5

12. Discuss BOREHOLE LOGS 5

13. Determine the area ratio for the following soil samplers and comment on the nature of soil sample expected in each sampler

(a) Core Cutter 165 mm OD 150 mm ID

(b) Split barrel 51 mm OD 35 mm ID 5

14. Discuss in brief the various methods used to improve the expansive soils. 5

15. Discuss various methods of grouting in brief. 5