Cyclic soil plasticity

Student: Damian Grant
Supervisors: Prof. F. Auricchio, Dr. J. Berrill



Accurate constitutive models for cyclic soil plasticity are an important requirement in many engineering applications. Models based on the Modified Cam-Clay yield criterion, an associative flow rule, a nonlinear hyperelastic stress-strain law and an appropriate hardening equation, are effective for cases of monotonic loading, but inaccurate for cyclic loading conditions.

In this dissertation, a Modified Cam-Clay model is presented, followed by two separate approaches extending the model's effectiveness to cyclic loading histories. In the first approach, an anisotropic Bounding Surface model with a vanishing elastic region and a discrete relocation of the back stress tensor is implemented. Secondly, the Modified Cam-Clay model is reformulated in a Generalised Plasticity framework, in which a yield function defines the boundary between elastic and inelastic states, and a limit function defines admissible and inadmissible states.

For each approach, a time discrete version of the model is presented, and a solution algorithm based on a return mapping algorithm is derived. The models are tested in a finite element setting, and behaviour under different loading histories is compared. It is found that both the Bounding Surface and Generalised Plasticity models provide some advantages over the original model, but suffer from several flaws which need to be addressed in future formulations.

You may download a digital version of this MSc dissertation here.