A sample of clay is set up in a triaxial apparatus and anisotropically compressed, without allowing radial strains, to a vertical effective stress σ‘ = 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 Ko = 0.65. 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 Ko is now equal to 1.0.
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 = 0.9, A= 0.19, K = 0.06, N = 2.88, and G' = 2500 kPa.
Compare the strengths that would be measured in conventional drained and undrained triaxial compression of the clay starting from state D.
