EVOLUTION CHARACTERISTICS OF ELASTIC MODULUS AND ENERGY OF BIOTITE QUARTZ SCHIST UNDER CYCLIC LOADING AND UNLOADING TEST

The biotite quartz schist is a typical anisotropic rock. To study its damage evolution law and anisotropic characteristics, equal plastic strain cyclic loading and unloading tests were carried out on samples with schistosity angles of 0°, 45°, and 90°. The results show that the failure modes of specimens with different schistosity plane angles are distinct, with tension fracture phenomena observed in the 0°schistosity samples and shear fracture phenomena in the 45°schistosity samples being particularly pronounced. With an increase in plastic strain, the elastic modulus of biotite quartz schist first strengthens and then weakens. This phenomenon is more evident under high confining pressure. The turning point in the weakening stage is consistent with the corresponding plastic strain when the initiation strength is stable. As an evaluation index of rock damage and the deterioration process, the elastic modulus is less affected by the angles of schistosity than the integrity coefficient. In the process of the internal energy evolution of rock, the relationship between dissipated energy and the angles of schistosity is 0°>90°>45°. The relationship between the decreasing rate of dissipated energy and elastic energy is 45°>90°>0°. The corresponding plastic strain of the elastic energy and dissipated energy when it evolves to a stable state is the same as that of damaged strength. This study explores the mechanical behavior of damage evolution of biotite quartz schist through the analysis of the evolution characteristics of elastic modulus and energy.