A critical state constitutive model for clean and silty sand

Abstract

The mechanical behavior of silty sand is highly dependent on the percentage of fines in addition to the packing density and confining pressure. Properly modeling the diverse behavior of silty sand remains an area of difficulty and uncertainty. This paper presents an attempt to formulate a critical state-based constitutive model for sand with varying fines content based on several new laboratory findings. A marked feature of the model is a unified description of the state-dependent elastic modulus as well as a unified description of plastic hardening modulus such that only one set of elastic and hardening parameters is required for sand with different fines contents. The model is calibrated and validated using the results from a structured experimental program. It shows that the model can produce reasonably good predictions for undrained shear responses of sand specimens under a range of void ratios, confining stresses and fines contents. In particular, it successfully predicts the laboratory observation that under otherwise similar conditions, the presence of non-plastic fines increases the liquefaction susceptibility of sand.