# Semester Geotechnical Engineering June 2011

PART A

I. (a) Define sensitivity and thixotropy

(b) Differentiate between submerged unit weight and saturated unit weight.

(c) State effective stress law. Explain the significance.

(d) Explain pressure bulb.

(e) Is zero air voids line is a straight line? Substantiate your answer.

(f) Differentiate between over consolidated and under consolidated clay.

(g) Sketch different types of slope failures.

(h) State Mohr-Coulumb failure criteria.

PART B

II.  (a) From first principle derive the relation e x Sr – W x Gs

(b) Give three examples each for residual soil and transported soil

OR

III. Calculate the dry unit weight, the saturated unit weight and the buoyant unit weight of a soil having void ratio 0.7 and specific gravity 2.72. Also calculate the unit weight and water content at a degree of saturation of 75%

IV. In a falling head permeability test the initial head of lm dropped to 0.35 m in 3 hours, the diameter of the standpipe being 5 mm. The soil specimen was 200 mm long by 100 mm in diameter. Calculate coefficient of permeability.

OR

V. A load of 1500 kN is carried on a foundation 2m square at a shallow depth in a soil mass. Determine the vertical stress at a point 5 m below the centre of the foundation.

VI. The following results were obtained from a standard light compaction test

Mass (g)                                 2010    2092      2114     2100     2055

Water content (%)             12.8     14.5      15.6      16.8       19.2

Plot dry density – water content curve and give OMC. Plot also zero air voids curve and 90% saturation curve.

OR

(VII). In an odometer test a specimen of saturated clay 19 mm thick reaches 50% consolidation in 20 minutes. How long would it take a layer of this clay 5 m thick to reach same degree of consolidation under the same stress and drainage conditions?  How long would it take the layer to reach 90% consolidation?

(VIII). What is the shear strength in terms of effective stress on a plane within a saturated soil mass at a point where the total normal stress in 295 kN/m2 and the pore water pressure 120 kN/m2? The effective stress parameters for the soil are C’-\2kNIm2 and </>’ = 30°

IX. Explain Bishop’s slope stability analysis.