  In this paper, we develop an elasto-viscoplastic (EVP) model for clay using
the non-associated flow rule. This is accomplished by using a modified form of
the Perzyna's overstressed EVP theory, the critical state soil mechanics, and
the multi-surface theory. The new model includes six parameters, five of which
are identical to those in the critical state soil mechanics model. The other
parameter is the generalized nonlinear secondary compression index. The EVP
model was implemented in a nonlinear coupled consolidated code using a
finite-element numerical algorithm (AFENA). We then tested the model for
different clays, such as the Osaka clay, the San Francisco Bay Mud clay, the
Kaolin clay, and the Hong Kong Marine Deposit clay. The numerical results show
good agreement with the experimental data.
