Problem $2(2\mathrm{.}5$ pts$)$

A consolidated drained triaxial test is performed on a specimen of dense sand. The test failed along a

well$-$defined failure plane at an angle of $62\backslash$deg with the horizontal. Assuming that the test was performed

in the conventional way, i$.$e$.$ maintaining the chamber pressure constant while increasing the axial

stress, find the effective confining pressure of the test if the principal stress difference $($s $1-$ s $3)$ at

failure was $115$ kPa.

Hint: $($s$1-$ s$3)=($s$1-$ s $3)$