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GATE 2023 CE (CE1) – Question 18

Geotechnical Engineering · Shear strength, Mohr circle, stress-strain characteristics, stress paths · 1 mark · Multiple choice

A possible slope failure is shown in the figure. Three soil samples are taken from different locations (I, II and III) of the potential failure plane. Which is the most appropriate shear strength test for each of the sample to identify the failure mechanism? Identify the correct combination from the following options:
P: Triaxial compression test
Q: Triaxial extension test
R: Direct shear or shear box test
S: Vane shear test

a slope with a circular potential failure plane. Sample I is at the toe (at the bottom left), sample II is at the bottom of the circle and sample III is behind the crest, at the top of the failure plane.
  1. I-Q, II-R, III-P
  2. I-R, II-P, III-Q
  3. I-S, II-Q, III-R
  4. I-P, II-R, III-Q

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Show answer and explanation

Correct answer: (A) I-Q, II-R, III-P

Explanation

Behind the crest (III) the soil is in the active state, where the vertical stress is the major principal stress, as in a triaxial compression test (P). Along the bottom of the failure surface (II) the soil is sheared along a near-horizontal plane, as in the direct shear test (R). At the toe (I) the soil is pushed up and out, the passive state, where the horizontal stress is the major principal stress, as in a triaxial extension test (Q).