Mechanical properties and energy damage evolution mechanism of deep-buried carbonaceous phyllite

In order to study the anisotropy of the water-softening damage characteristics and the micro-layered structure of deep-buried carbonaceous phyllite, rock mechanical tests of carbonaceous phyllite were conducted under different bedding directions and different water contents. Based on the energy damage evolution mechanism, the influences of bedding direction and water content on the energy storage and energy release mechanism of phyllite are analysed. The results suggest that the anisotropic characteristics and water-softening effects of deep-buried carbonaceous phyllite are inherent characteristics attributed to sedimentary beddings, layered lamellar minerals and high content of clay minerals inside the carbonaceous phyllite. The failure mechanism and the anisotropic strength of phyllite are dominated by the weak cementation between the bedding surfaces. This weak-surface effect increases with the decrease of confining pressure. With the increase of water content, the mechanical properties and brittleness of phyllite are weakened, and the macroscopic failure angle is increased, which results in the decrease of tensile failure and the increase of shear failure. Based on the energy evolution mechanism and the S-shaped curves between elastic energy and dissipated energy, the gradual failure process of rocks is divided into four stages. Based on the energy damage evolution mechanism, the energy mechanism and its damage evolution mechanism of rocks' two typical failure modes, type I and type II, are studied. It is found that the bedding direction and water content both have great influence on the energy storage capacity of phyllite. The bedding direction has a small influence on the energy release mechanism and damage evolution mechanism of phyllite. The energy storage and energy release mechanism of phyllite are more sensitive to water content than to bedding direction.