Abstract: This paper intends to describe the confining pressure correlation of the mechanical behavior of sand in a reasonable way. Firstly, the relationship between the mechanical properties of sand and the confining pressure is analyzed and summarized. As the confining pressure decreases, the basic mechanical properties of sand show a stronger confining pressure dependence, the critical state stress ratio changes from a constant to a sensitive variable with the confining pressure, and the dilatancy changes from gentle to a sharp increase. Then, under the theoretical framework of unified hardending model for clays and sand, namely CSUH model, the occlusal stress parameters are introduced to describe the critical state strength characteristics. The concept of uncoupled plastic volumetric strain is proposed, and the mechanism of strong dilatation under low confining pressure is explained from the microscopic level. Based on the analysis of the influence of confining pressure on compression-shear coupling, the expression of uncoupled plastic volumetric strain is constructed, and then a unified hardening (UH) model of sandy soil which can consider the confining pressure effect is established. Compared with CSUH model, UH model considering confining pressure effect only adds two parameters, and the parameters are easy to determine. Finally, the rationality and applicability of the model are verified by comparing with the experimental data and the prediction results of CSUH model.

Key words: sand, confining pressure, occlusion, uncoupled, unified hardening (UH) model