Modified cutting-plane integration scheme for elasto-viscoplastic models

The elasto-viscoplastic model can be regarded as a combination of the modified Cam-clay model and the overstress theory. Firstly, the stress-strain formulas for the model are rearranged, in which an evolution equation for the hardening parameter of dynamic loading surface is deduced based on the overstress theory. Secondly, the rearranged stress-strain formulas are numerically implemented by the cutting-plane integration scheme. In an elastic prediction process, the viscoplastic strain rate is assumed to be constant, which guarantees the deviation of the current stress state from dynamic loading surface due to time increments. In a plastic corrector process, a Taylor series approximation of the dynamic loading function is used to obtain the increment of viscoplastic multiplier rate. Thirdly, an adaptive substepping method is proposed to maintain the accuracy and convergence of the proposed algorithm at a large loading step. Finally, the performances of the modified cutting-plane algorithm are analyzed by the calculated results of step-changed oedometer tests and undrained triaxial tests.