The energy dissipation process and dilation evolution of the rock subjected to incremental cyclic loading and unloading

Abstract Rock mass around underground engineering is sometimes subjected to varying degrees of cyclic load, such as geological tectonic movements, seismic events, excavation, and support of underground caves, which induces some certain deterioration for rock mass strength due to energy dissipation and cumulative micro fractures. Some key scientific questions include the mechanism of energy dissipation and the law of strength parameters' evolution of rock subjected to cyclic increasing loading. In order to clarify the relations between rock energy dissipation and the dilation evolution during the process of failure, an incremental cyclic loading mode is proposed and adopted in uniaxial and triaxial tests. First, the dilation test method and procedure are proposed in this article to improve the test success rate. Granite gneiss specimens sampled from the Southern Xinjiang region were tested to obtain the mineral composition's fundamental mechanical parameters. The incremental cyclic loading uniaxial and triaxial tests are carried out under confining pressure from 0 MPa to 50 MPa during pre-peaking and post-peaking strength periods. From the viewpoint of energy dissipation, the damage variable is defined, and its relationships with the energy dissipation parameters and principal strain(residual strain and residual shear strain) are deeply analyzed during cyclic loading. Moreover, the confining pressure effect on the energy parameters and variables was studied as well. For each cyclic loading and unloading, the relationship between residual volumetric strains versus residual principal strains was acquired from the curves, which provides the fundamental data for further dilation property research. According to the evolution law of damage variable versus plastic shear strain curves, the relationships between energy dissipation ratio and shear dilation angle are constructed. In summary, the research reveals that the damage evolution process of rock is based on the energy dissipation mechanism, and these relationships with its dilation to failure show important significance, which sets up a bridge between the energy mechanism and dilation during the failure process.