GATE 2016 CE (CE1) – Question 54
A drained triaxial compression test on a saturated clay yielded the effective shear strength parameters as c' = 15 kPa and ϕ' = 22o. Consolidated Undrained triaxial test on an identical sample of this clay at a cell pressure of 200 kPa developed a pore water pressure of 150 kPa at failure. The deviator stress (expressed in kPa) at failure is ______.
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Correct answer: 100 to 110
Explanation
Effective confining pressure is σ3-prime=200−150=50kPa. Mohr–Coulomb gives qf=2σ3-prime sinφ/(1−sinφ)+2c-prime cosφ/(1−sinφ). With c-prime15kPa and φ22°, this gives **104.38kPa**. Deviator stress is identical in total and effective stresses because the same pore pressure subtracts from both principal stresses.