Abstract:

Layered rock masses are often encountered in deep engineering. Due to the influence of high stress, rock mass hazards induced by layered structures often occur in engineering activities. This is closely related to the true three-dimensional high-stress environment and layered structures in deep engineering. For this reason, the test considering the orientation of schistosity was carried out under true triaxial compression based on a layered hard schist taken from a deep metal mine, and the deformation, strength and fracture characteristic of the samples with two schistosity loading orientations were obtained under different stress conditions. The results show that the mechanical properties of the hard schist are greatly affected by schistosity loading orientation and stress conditions. More specifically, when σ₂ is parallel to the strike of schistosity, the brittleness of the sample is stronger, and the smaller the σ₃, the stronger the brittleness. The strength of the sample is higher when σ₂ is perpendicular to the strike of schistosity, but the sensitivity of the increase in strength with the increase of  σ₃ is weaker. When σ₂ is parallel to the strike of schistosity, the shear failure along the schistosity prevails. When σ₂ is perpendicular to the strike of schistosity of the specimen, the tensile failure through the schistosity mainly occurs at a low σ₃ , and it transforms into shear failure along the schistosity at the high σ₃ . The test results have certain enlightenment significance for the stability evaluation of steep layered hard rock engineering: when the included angle between schistosity strike and tunnel axis is small, the normal stress release degree of schistosity of shallow rock is high, and brittle failure controlled by schistosity structure is easy to occur; on the contrary, the rock mass is relatively more stable when the included angle is large.

Key words: hard schist, multiaxial compression, schistosity orientation, mechanical properties