Question

A consolidated drained (CD) triaxial test was carried out on a sand sample with the known effective shear strength parameters,

\( c' = 0 \quad \text{and} \quad \phi' = 30^\circ \)

. In the test, prior to the failure, when the sample was undergoing axial compression under constant cell pressure, the drainage valve was accidentally closed. At the failure, 360 kPa deviatoric stress was recorded along with 70 kPa pore water pressure. If the test is repeated without such error, and no back pressure is applied in either of the tests, what is the deviatoric stress (in kPa, in integer) at the failure?

Hint:

In triaxial testing, when pore water pressure is included, the total stress at failure consists of both deviatoric stress and pore water pressure. When the drainage valve is closed, pore water pressure must be accounted for, but in the corrected test, with no pore water pressure, the deviatoric stress equals the total stress minus the pore pressure.

Answer 1

Correct Answer: 500