Exercises

E$5\mathrm{.}1.$ A sample of clay is set up in a triaxial apparatus and anisotropically compressed, without allowing radial strains, to a vertical effective stress ${}_v^{\text{'}}=156$kPa. It is found that the value of the earth pressure coefficient $($ratio of horizontal to vertical effective stresses$)$ measured in this process is $K_0=0\mathrm{.}65.$ The sample is then unloaded to a vertical effective stress of $100$ kPa $($point $A)$ and allowed to reach equilibrium with zero pore pressure. It is found that $K_0$ is now equal to $1\mathrm{.}0.$

The deviator stress is now increased to $60$ kPa without allowing drainage $($point $B).$ Without changing the total stresses, drainage is now permitted, and the pore pressure is allowed to dissipate. It is observed that yield occurs during this process $($point $C)$ and that the final equilibrium state at zero pore pressure is point $D.$

Estimate the axial and radial strains occurring on each stage $AB,BC,$ and $CD$ of the test. Assume that the behaviour of the clay can be described by the Cam clay model with values of soil parameters $M=0\mathrm{.}9,=0\mathrm{.}19,=0\mathrm{.}06,N=2\mathrm{.}88,$ and $G^{\text{'}}=2500$kPa.

Compare the strengths that would be measured in conventional drained and undrained triaxial compression of the clay starting from state $D.$