Question

a cu triaxial test (axial compression) on a specimen of saturated over-consolidated clay was carried out under a cell pressure of 500 kn/m2. consolidation took place against a back pressure of 209 kn/m2. the principal stress difference at failure was 535 kpa and the pore pressure reading at failure was 129 kpa. a companion drained test (cd) performed on an identical sample of the same clay at a consolidation pressure of 150 kpa (back pressure was zero) shows that the friction angle of the sample is 19 degrees. (a) how much is the undrained cohesion (cu) of the sample? (kpa)

Answer 1

The undrained cohesion (Cu) of the clay sample from the triaxial test can be calculated using the given cell pressure, principal stress difference at failure, and pore pressure, applying the total stress at failure formula and solving for Cu.

Step-by-step explanation:

To calculate the undrained cohesion (Cu) of the saturated over-consolidated clay from a triaxial test in axial compression, we can use the provided data. The cell pressure is given as 500 kN/m2 and the principal stress difference at failure is 535 kPa. The undrained cohesion can be calculated using the formula for total stress at failure, which is σ1 - σ3 = 2Cu + (σ3 - u), where σ1 is the major principal stress, σ3 is the cell pressure, and u is the pore water pressure at failure.

By rearranging the formula and solving for Cu, we get Cu = (σ1 - σ3)/2 - (σ3 - u)/2. Substituting the given values, Cu = (535 kPa)/2 - ((500 kN/m2 - 129 kPa)/2), we get the undrained cohesion Cu in kPa.