15 questions. Tap an option to check it instantly, then read the solution.
Practice SSC JE and other civil engineering exam questions on the shear strength of soils: the Mohr–Coulomb failure criterion, Mohr circles, cohesion and angle of internal friction, effective stress, and the direct shear, triaxial (UU, CU, CD), unconfined compression and vane shear tests. Tap an option to check it, then open the full explanation for each question.
Question 1Medium
Which of the following statements are correct with respect to Mohr–Coulomb failure criteria on soils? I. Mohr failure envelope is approximated as a straight line but in actual, it is curved. II. Mohr failure envelope is approximated as a curved line but in actual, it is straight. III. The Mohr circle drawn for soil cannot cross the Mohr failure envelope. IV. Cohesion c and angle of internal friction φ are fundamental properties of soil and are independent of testing conditions.
The true envelope is slightly curved but is taken as a straight line (I true). A Mohr circle cannot cross the envelope, because that would mean a stress state beyond failure (III true). c and φ depend on drainage and test conditions (IV false).
Question 2Medium
According to the Mohr–Coulomb failure criterion in soils, which of the following statements are INCORRECT? A. Shear strength is attributable to the interlocking of soil particles and cohesion. B. Shear strength is only attributable to the internal friction between particles. C. The Y-intercept represents friction of soils. D. The Mohr–Coulomb failure envelope is a straight line.
Strength comes from cohesion plus friction/interlocking, not friction alone (B incorrect). The y-intercept of the envelope is cohesion c, not friction (C incorrect). A and D are correct.
Question 3Easy
In the direct shear test conducted on soils, a proving ring is used to ______.
The proving ring is a calibrated steel ring; its deflection (read on a dial) gives the shear load on the specimen.
Question 4Medium
A sample of soil failed in a triaxial test under a deviator stress of 200 kN/m² when the confining pressure was 100 kN/m². If, for the sample, the confining pressure had been 200 kN/m², what would have been the deviator stress at failure? (Assume φ = 0.)
Answer: B. When principal stresses act along three mutually perpendicular directions
Triaxial stress means non-zero principal stresses in all three mutually perpendicular directions.
Question 7Medium
A sample of soil failed in a triaxial test under a deviator stress of 200 kN/m² when the confining pressure was 100 kN/m². For the sample, if the confining pressure had been 200 kN/m², what would have been the deviator stress at failure? Assume c = 0.
c = 0 ⇒ \(\sigma_1/\sigma_3 = \tan^2(45^\circ+\phi/2)\) is constant = 300/100 = 3 (φ = 30°). With σ₃ = 200, σ₁ = 600, so σd = 400 kN/m².
Question 8Easy
Identify the instrument used for finding the shear strength of soil that consists of a loading frame operated by a hand screw, a proving ring with a dial, a deformation dial gauge and conical seatings holding a cylindrical soil specimen without any surrounding cell.
A cylindrical specimen between conical seatings, loaded by a hand-operated frame with a proving ring and dial gauge and with no confining cell, is the unconfined compression test apparatus.
Question 9Easy
If the cohesion value of soil is zero, the Mohr envelope will pass through: