DHARMSHEARING STRENGTH OF SOILS 315
8.8 Explain the shear characteristics of sand and normally loaded clays.
(S.V.U. (B.E.) (R.R.)—May, 1971)
8.9 (a) What is the effect of pore pressure in strength of soils?
(b) Explain Coulomb’s law for shearing strength of soils and its modification by Terzaghi.
(S.V.U.—B.E. (N.R.)—May, 1969)
8.10 A granular soil is subjected to a minor principal stress of 200 kN/m^2. If the angle of internal
friction is 30°, determine the inclination of the plane of failure with respect to the direction of the
major principal stress. What are the stresses on the plane of failure and the maximum shear
stress induced?
8.11 Samples of compacted, clean, dry sand were tested in a shear box, 6 cm × 6 cm, and the following
observations were recorded:
Normal load (N): 100 200 300
Peak shear load (N): 90 180 270
Ultimate shear load (N): 75 150 225
Determine the angle of shearing resistance in (a) the dense state and in (b) the loose state.
8.12 An embankment consists of clay fill for which c′ = 25 kN/m^2 and φ = 27° (from consolidated-
undrained tests with pore-pressure measurement). The average bulk unit-weight of the fill is
2 Mg/m^3. Estimate the shear-strength of the material on a horizontal plane at a point 20 m
below the surface of the embankment, if the pore pressure at this point is 180 kN/m^2 as shown by
a piezometer.
8.13 The following data are from a direct shear test on an undisturbed soil sample. Represent the
data by a Mohr Circle and compute the principal stresses and direction of principal planes:
Normal pressure = 16.2 kN/m^2 ; Tangential pressure = 14.4 kN/m^2 ,
Angle of internal friction = 24°; c = 7.2 kN/m^2. (S.V.U.—B.E. (N.R.)—Sept., 1967)
8.14 From a direct shear test on an undisturbed soil sample, the following data have been obtained.
Evaluate the undrained strength parameters by plotting the results. Also draw a Mohr Circle
corresponding to the second test. Hence determine the major and minor principal total stresses
for the second test.
Normal stress ... 70 96 114
kN/m^2
Shear stress ... 138 156 170
kN/m^2 (S.V.U.—B.E. (N.R.)—May, 1975)
8.15 Two samples of a soil were subjected to shear tests. The results were as follows:
Test No. σ 3 (kN/m^2 ) σ 1 (kN/m^2 )
1 100 240
2 300 630
If a further sample of the same soil was tested under a minor principal stress of 200 kN/m^2 , what
value of major principal stress can be expected at failure?
8.16 A shear box test carried out on a soil sample gave :
Test No. Vertical stress Horizontal shear stress
(kN/m^2 ) (kN/m^2 )
1 100 80
2 200 144
3 300 216