Influence of Intermediate Principal Stress on the Strength and Dilatancy Behavior of Rockfill Material

The mechanical behaviors of rockfill materials at a comparatively low pressure are very important (e.g., for the stability of the top part and the slope of rockfill dams). In addition, the stress conditions of rockfill dams are unlikely to be axisymmetric but are three-dimensional. Because of this, the influence of the intermediate principal stress has to be taken into consideration in design. This paper presents a study on the effect of intermediate principal stress on the strength and dilatancy behavior of rockfill material at a comparatively low pressure. A series of constant b-value tests were carried out on rockfill materials commonly used for earth dam construction. Using the test data, the influences of the b-value on the peak friction angle, critical-state friction angle, and maximum dilatancy angle of rockfill materials were investigated. A revised relative dilatancy index was proposed for rockfill material to describe the change in the shear strength with the intermediate principal stress. The relationship among the incremental friction angle, the maximum dilatancy angle, and the b-value was examined. A linear relationship between the incremental friction angle and the revised relative dilatancy index was established by considering the effect of the b-value. The predictions given by this relationship agree well with experimental data. Furthermore, the b-value can influence the particle breakage of rockfill materials, indicating that such breakage is dependent on the stress path.