Practical Estimation of Compression Behavior of Clayey/Silty Sands Using Equivalent Void-Ratio Concept

Clayey/silty sands are widespread as naturally sedimentary soils such as marine deposits in estuaries and offshore locations. They belong to a unique class of gap-graded soils featuring a deficiency of certain range of particle sizes and behave differently from those containing pure sand aggregates. The fines improve the stiffness of host sands, which reduces the postconstruction settlement and arching effect of foundations and dams. In this study, a simple yet effective compression model is proposed for clayey/silty sands using the equivalent void-ratio concept. A structure parameter is incorporated into the model to denote the contribution of fines on the effective force chains of gap-graded mixtures. The structure parameter is affected by the particle-size distribution and basic features of sand aggregates. It can be approximated by a constant value, which represents a combination effect of the influence factors. The limit (inactive) void ratio of clayey/silty sands decreases linearly with the increase of fine content and the structure parameter. The proposed model contains only three model parameters, all of which have clear physical meanings and can be readily calibrated based on two conventional compression tests. Simulations using the newly proposed model revealed that it is versatile to capture key features of gap-graded mixtures, including the effect of initial void ratio, interaggregate void ratio, and fine content. The performance of the proposed model is verified with tests data for six clayey sands and five silty sands (or sandy gravel). The differences between the test data and model predictions for both clayey sands and gap-graded granular mixtures are marginally small. The model can be practically useful for predicting the deformation of clayey/silty sands.