Energy evolution mechanism of the mechanical and creep properties of layered phyllite under uniaxial compression and creep tests

To study the anisotropic mechanical behaviour and creep characteristics of layered rock masses, this study conducts uniaxial compression and uniaxial compression creep tests on phyllite with bedding angles of 0°, 22.5°, 45°, 67.5° and 90°. Based on the energy calculation theory, the total strain energy, elastic energy and dissipated energy of rock samples under different loads are obtained. The results indicate that the total energy, elastic energy, dissipated energy and elastic energy ratio at the peak strength of the uniaxial compression stress–strain curve of the rock sample first decrease and subsequently increase with increasing bedding angle. The post-peak elastic energy mutation amplitude and dissipated energy mutation amplitude have the same trends. Thus, the bedding angle has a significant effect on the energy accumulation and dissipation of layered phyllite. In a uniaxial compression creep test, in addition to the first-stage loading, the total energy, elastic energy and dissipated energy of rock samples increase with increasing loading stress. At the peak point of the creep stress–strain curve, the total energy, elastic energy, dissipated energy, elastic energy ratio of the rock samples and the total energy absorbed by the rock samples under different loading stresses also first decrease and subsequently increase with increasing bedding angle, which indicates the anisotropic creep characteristics of the energy evolution of the layered rock mass. Compared with the uniaxial compression, the total energy of the layered rock mass under uniaxial creep stress increases by 1.13 ~ 1.91 times, and the dissipated energy increases by 2.44 ~ 8.18 times. Moreover, the failure mode of the rock sample produces more secondary cracks accompanied by local collapse. Based on these results, the influence of the anisotropic creep characteristics of layered rock masses on engineering cannot be ignored.