UNDRAINED PLASTIC MODULUS FROM ORIGINAL CAM CLAY

One aspect of the original Cam-clay model is that the derived undrained stress-strain curve can be expressed in closed form and used to determine a finite value of stiffness at epsilon = 0 that is equivalent to an undrained plastic modulus (or E(u)) for normally consolidated clays. With respect to soil behavior, this predicted modulus in no way represents the initial modulus E(max) that is fundamental and obtained from resonant column tests at small-strain levels (epsilon < 10(-5)), but interestingly corresponds to the apparent initial undrained stiffness obtained from a hyperbolic fit of isotropically consolidated undrained triaxial stress-strain data over the range of intermediate to large strains (0.001 < epsilon < 0.10). A review of triaxial and consolidation data from 17 clays supports this observation.