SPSC 2014 Assistant Engineer (Civil) BPS-17, Public Health Engineering Department (2014) — Soil Mechanics and Foundation Engineering Paper

Assistant Engineer (Civil) BPS-17, Public Health Engineering Department (2014) — Soil Mechanics and Foundation Engineering. Competitive examination for the post of Assistant Engineer (Civil) BPS-17 in PHED, Government of Sindh · Monday 27 January 2014, 10:00 am to 1:00 pm · Max marks 100. Attempt any five questions. Figures in the paper are described in words.

1. 1(a) Explain the importance of Soil Mechanics in Civil Engineering. What are the major soil deposits in Sindh Region and their characteristics? (08) (b) There are two borrow areas A and B which have soils with void ratios of 0.80 and 0.70 respectively, and specific gravity of 2.65. The in-place water content is 20% and 15% respectively. The fill at the end of construction will have a total volume of 10,000 m³, bulk density of 2 Mg/m³ and a placement water content of 22%. Determine the volume of soil required to be excavated from both areas. (12)

2. 2(a) A drainage pipe beneath a dam has clogged with sand whose coefficient of permeability is found to be 8.0 m/day. The average difference in head water and tail water elevation is 21.2 m, and it has been observed that there is a flow of 162 litres per day through the pipe. The pipe is 94.3 m long and has a cross-sectional area of 180 sq. cm. What length of the pipe is filled with sand? (10) (b) An aquifer is inclined at 20° to the horizontal. The difference of water levels in two observation wells at a horizontal distance of 70 m is 6 m. Determine the discharge through the aquifer per unit width if K = 0.8 mm/sec. The depth of aquifer normal to the direction of flow is 4.0 m. (10)

3. 3(a) Explain different types of lateral earth pressure and their utilization in design of retaining walls. (08) (b) On a site of a building construction, a cut of 4 m depth was made in a soil. The lab tests show that the soil has cohesion = 20 kN/m², angle of internal friction = 12° and unit weight = 18 kN/m³. Determine the stresses at the top and bottom of the cut. Also determine the maximum depth of potential crack and maximum depth of unsupported excavation. (12)

4. 4(a) Discuss the standard penetration test. What are the various corrections? What is the importance of the test in geotechnical engineering? (09) (b) Two plate load tests were conducted at the level of a prototype foundation in cohesionless soil close to each other. If a footing is to carry a load of 1000 kN, determine the required size of footing for the same settlement of 25 mm. (11) Test 1: plate 0.3 m × 0.3 m, load 30 kN, settlement 25 mm. Test 2: plate 0.6 m × 0.6 m, load 90 kN, settlement 25 mm.

5. 5(a) Describe the various purposes for which pile foundations are resorted to. (08) (b) It is proposed to provide pile foundation for a heavy column; the pile group consists of 4 piles placed at 2.0 m centre to centre, forming a square pattern. The underground soil is clay, having undrained cohesion of 6 t/m² at the surface and 10 t/m² at depth 10 m. Compute the allowable column load on the pile cap if the piles are circular, 0.5 m in diameter and 10 m long. (12)

6. 6For the earth retaining structure shown, construct the earth pressure diagram for the active state and determine the total thrust per unit length of the wall. (20) Figure: a vertical wall H = 10 m retaining sand (G = 2.65, e = 0.65, φ = 30°) with a horizontal surface carrying a surcharge q = 14 kN/m²; the ground water table is 3.0 m below the surface.

7. 7The observed standard penetration test value in a deposit of fully submerged sand was 45 at a depth of 6.5 m. The average effective unit weight of the soil is 9.69 kN/m³. The other data are: hammer efficiency Eh = 0.8, drill rod length correction factor Cs = 0.9 and borehole correction factor Cb = 1.05. Determine the corrected SPT value for standard energy: (a) Res = 60% and (b) Res = 70%. (20)

8. 8A sample of wet silty clay soil 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 (a) dry density (b) porosity (c) void ratio and (d) degree of saturation. (20)