GATE 2022 CE (CE2) – Question 33
In a triaxial unconsolidated undrained (UU) test on a saturated clay sample, the cell pressure was 100 kPa. If the deviatoric stress at failure was 150 kPa, then the undrained shear strength of the soil is _________ kPa. (in integer)
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Correct answer: 75
Explanation
For saturated clay in a UU test, the total-stress friction angle is zero. The undrained strength is the failure Mohr-circle radius, $c_u=(\sigma_1-\sigma_3)/2$.
The deviator stress is already 150 kPa, so $c_u=150/2=\mathbf{75}$ kPa. Cell pressure shifts the circle without changing its radius.