Abstract: Dilatancy angle is commonly used to describe the expansion behaviours of rock. Continuum theory generally assumes that the value of dilatancy angle is 0° for the materials obeying the non-associated flow rule, but for those materials obeying the associated flow rule the dilatancy angle is a constant value equal to internal friction angle. The full volumetric curves of triaxial compression show that volumetric dilatancy is highly dependent on the confining pressure and plastic parameters. In a full failure process, not only the characteristic strength but also characteristics of dilatancy properties behave in a nonlinear manner with change of confining pressure and plastic parameters,. Employing plasticity theory and the nonlinear fitting method, a double parameters’ dilatancy angle model is developed, based on damage control triaxial loading and unloading cycle test data of Jinping marble, to take into account the effects of the confining pressure and plastic parameters. The model reveals that the dilatancy behaviors of marble as well as similar hard rocks are mainly governed by the confining pressure and plastic parameters during a failure process, which shows significant nonlinearity, and the dilatancy angle rapidly increases to the peak and then decreases gradually with increasing plastic deformation. The proposed double-parameters nonlinear dilatancy angle model can be used to describe the volumetric dilatancy properties, helping understand the mechanism of surrounding rock failure around underground openings and predict the range of expansion volume. In addition, the proposed model has theoretical and practical bearings on the design of supporting structures in underground rock engineering.

Key words: shear dilatancy angle, damage-control, plastic parameter, triaxial loading and unloading cycle test, nonlinear dilatancy angle model