Question

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 _________ \text{ kPa}. (in integer)

Hint:

In a UU test, the undrained shear strength is half the difference between the deviatoric stress and the cell pressure.

Answer 1

Correct Answer: 75

In an unconsolidated undrained (UU) test, the undrained shear strength \( \tau_u \) is given by:
\[ \tau_u = \frac{\sigma_1' - \sigma_3'}{2} \] Where:
- \( \sigma_1' = \text{deviatoric stress at failure} = 150\ \text{kPa} \)
- \( \sigma_3' = \text{cell pressure} = 100\ \text{kPa} \)
Substitute the values:
\[ \tau_u = \frac{150 - 100}{2} = \frac{50}{2} = 75\ \text{kPa} \] Thus, the undrained shear strength of the soil is:
\[ \boxed{75\ \text{kPa}} \]