SPSC 2011 Assistant Engineer / Assistant Executive Engineer (Civil) BPS-17, Engineers Cadre CCE (2011) — Soil Mechanics & Foundation Engineering Paper

Assistant Engineer / Assistant Executive Engineer (Civil) BPS-17, Engineers Cadre CCE (2011) — Soil Mechanics & Foundation Engineering. Combined Competitive Examination for Engineers Cadre · Saturday 26 March 2011, 10:00 am to 1:00 pm · Max marks 100. Attempt any 05 questions. Figures in the paper are described in words.

1. 1(a) A sample of wet silty clay has a mass of 126 kg. The following data were obtained from laboratory tests on the sample: wet density = 2.1 g/cm³, G = 2.7, water content w = 15%. Determine dry density, porosity, void ratio and degree of saturation for the sample. (10) (b) The moisture content of an undisturbed sample of clay belonging to a volcanic region is 265%, with 100% saturation. The specific gravity is 2.5. The dry unit weight is 3.3 kN/m³. Determine the saturated unit weight, the submerged unit weight and void ratio. (10)

2. 2A reinforced concrete water tank of size 8 m × 8 m resting on the ground surface carries a uniformly distributed load of 2550 kN/m². Estimate the maximum vertical pressures at depths of 12 and 24 metres by point approximation. (20)

3. 3(a) Classify the sheet piles according to their materials. Discuss their advantages and disadvantages. (10) (b) A concrete pile of 40 cm diameter, carrying a safe load of 650 kN, is required to be driven into a homogeneous mass of cohesionless soil. A static cone penetration test conducted at the site indicates an average value of qc = 40 kg/cm² along the pile and 120 kg/cm² below the pile tip. Compute the length of the pile with Fs = 2.5. (10)

4. 4The depths of soil behind and in front of a rigid retaining wall are 8 m and 3 m respectively, both soil surfaces being horizontal. The appropriate shear strength parameters for the soil are cu = 30 kN/m² and φu = 22°, and the unit weight is 18 kN/m³. Using Rankine theory, determine the total active thrust behind the wall and the total passive resistance in front of the wall. (20) (The paper prints "3 cm".)

5. 5The liquid, plastic and shrinkage limits of a soil were reported at 60%, 30% and 20% respectively. The sample of soil has a volume of 40 cc at liquid limit. The volume of the soil sample is reduced to 23 cc at shrinkage limit. Determine the specific gravity of the solids. Also find the shrinkage ratio and volumetric shrinkage of the soil. (20)

6. 6(a) What do you know about friction Piles? (08) (b) Find the penetration depth for a 40 cm square R.C. pile driven through sea bed for a jetty structure to carry a maximum compression load of 600 kN and a net uplift load of 350 kN. The soil below the sea bed consists of a 10 m thick layer of saturated medium dense sand overlying dense sand and gravel. The average corrected SPT blows in the top 10 m sand are 12, and 40 in the bottom sand-gravel layer. No erosion is expected. The minimum safety factor should be 2.5 on the uplift load and 3.5 on the compression load. (12)

7. 7(a) Describe the causes of settlements and their effects on buildings. Discuss the remedial measures to prevent excessive total and differential settlements. (09) (b) For the soil profile shown, if a uniformly distributed load Δσ is applied at the ground surface, what is the settlement of the clay layer caused by primary consolidation if (i) the clay is normally consolidated, (ii) the pre-consolidation pressure σ'c = 200 kN/m², and (iii) σ'c = 160 kN/m²? [Use Cs = 1/6 Cc] (11) Figure: Δσ ≈ 90 kN/m² at the surface (faint on the scan); 2 m of sand (γd = 14 kN/m³) above the water table; 4 m of sand (γsat = 18 kN/m³); 4 m of clay (γsat = 19 kN/m³, void ratio e = 0.8, liquid limit = 40); sand below.

8. 8An embankment for road traffic is required to be constructed with top width 8 m, height 4 m and side slopes 1:1.5. The unit weight of soil under the worst condition is 21 kN/m³. Compute the vertical pressure at a depth of 6 m below the ground surface, on the central longitudinal plane of the embankment and below the toes of the embankment. (20)