Study on mechanical characteristics of phyllite by conventional triaxial compression under multi-factors coupling action.

Phyllite belongs to metamorphic soft rock and is often encountered during tunnel excavation, which brings inconvenience and safety problem to construction. The mechanical characteristics of phyllite are influenced by multiple factors. This study conducted conventional triaxial compression mechanical experiments on phyllite under the multi-factor coupling action, including confining pressure, water content state, and bedding angle, which purpose is to explore the evolution process and change law of phyllite under various influencing factors. The results indicate that the relationship between peak strength, elastic modulus and bedding angles follows a "W" shape (dry state) and a "U" shape (saturated state). The peak strength and elastic modulus of high confining pressure is always higher than that of low confining pressure, which can increase by 20.55%~55.44% (saturated) and 23.29%~102.22% (dry) in the peak strength, and 1.19%~22.40% (saturated) and 2.39%~22.45% (dry) in elastic modulus. The peak strength and elastic modulus of dry condition is generally higher than that of saturated condition. The crack initiation and damage of phyllite are affected by various influencing factors, resulting in the failure modes of phyllite are more complex. The failure modes of phyllite include slip shear failure, compression tensile shear failure, tension failure and composite failure.