Water Content and Bedding Angle Effects on the Mechanical Properties and Micro-/Macro-Failure Mechanism of Phyllite

The study of anisotropy and water degradation in phyllite is a prerequisite for excavation and support of phyllite tunnels. Previous studies have mostly analyzed the mechanical characteristics of phyllite under the action of water/laminae alone, but less research has been carried out on the macroscopic properties and microfracture evolution of phyllite under the action of coupled water-laminae. Therefore, the microstructure, mechanical behavior and fracture mode of phyllite were analyzed by polarized light and uniaxial experiments, and then SEM, acoustic emission (AE) and numerical tests of phyllite were carried out. The results indicate that (1) the elastic modulus of phyllite presents an asymmetric U-shape with bedding angle, with the maximum value of 0° and 90° and the minimum value of 60°. The peak strength shows two differentiation trends: U-shaped and nonlinear decreasing with bedding angle. (2) The peak strength and elastic modulus of phyllite are negatively correlated with water content. (3) The fracture mode of phyllite changes from compression shear failure to tensile failure with bedding angle. (4) The laminated structure and fish scale texture of phyllite tend to be discrete due to water erosion, which promotes the expansion of microcracks and weakens the mechanical parameters of the rock. (5) The change law of AE cumulative energy with bedding and water content is consistent with the change in macromechanical characteristics, which reveals the internal relationship between the progressive evolution of microcracks in rocks and macrofractures. The research results can provide an important reference for the construction scheme design, long-term stability, operation and maintenance of similar projects.