A unified critical state parameter model for sand and overconsolidated clay in the framework of subloading surface theory

Abstract

This paper presents a unified critical state parameter model for evaluating sand and overconsolidated clay, which is named as CASM-S. The model is formulated in terms of the modification of the clay and sand model, i.e., CASM, by incorporating the subloading surface theory with an overconsolidation state parameter R. Although the standard CASM proves to be useful in modelling overconsolidated clay and sand, the model (1) requires the rate of overconsolidated ratio to be constant which is in contrast to the observed behaviour of soils and (2) only allows elastic deformation to develop at the overconsolidated state that may underestimate the deformation corresponding to the peak stress or be unable to predict the actual stress path. By introducing a new material parameter u to those material properties of the standard CASM, the rate relationship of stress–strain for the CASM-S model is developed. The standard CASM can be either recovered or approximated as a special case of the overconsolidation state assumed in the CASM-S. The numerical integration of the newly proposed model is performed by the modified forward Euler method. Validation with undrained and drained overconsolidated clay and sand have demonstrated the capability of the CASM-S model to well predict the observed soil behaviours.