Estimation of the compression behavior of sandy clay considering sand fraction effect based on equivalent void ratio concept

Abstract

Abstract Sandy soils produced from offshore engineering and dredging activities usually possess a fine fraction beyond the “transitional fine content”. The soils have a wide range initial water content and sand fraction. Previous models based on mixture theory is not straightforward, and the effect of initial water content is not explicitly incorporated. To this end, a novel compression model is formulated by incorporating the equivalent void ratio into the tangent stiffness of clay matrix. The virgin compression behavior of clay matrix is captured by incorporating two physical variables, termed as the reference void ratio and the remolded yield stress, which are correlated with the initial water content of the clay matrix. The equivalent void ratio concept is then introduced by incorporating a structure variable which relies uniquely on the volume fraction of sand. The structure variable denotes the sand fraction effect linking to partial contacts and densified clay bridges between aggregates. It relies on basic features of sand, e.g., the particle shape and particle size distribution. Morphological analysis reveals that the model is versatile to capture the two basic features of the sandy clays, e.g., the increasing compressibility and decreasing remolded yield stress with rising initial void ratio of clay matrix, the sand fraction effect arising from the partial contacts and clay bridges between aggregates. The proposed model has five material constants, and only three oedometer tests are required for the calibrating these parameters. Validation of the model reveals that the model is effective to reproduce the compression behavior of sandy soils with a wide range of initial void ratio and sand fraction.