Experimental analysis of failure process in soft-hard combined rock masses at different inclination angles

In order to investigate the influence of the inclination angle of soft rocks on the evolution process of composite rock mass rupture, this paper conducted uniaxial compression experiments on composite rock masses with different inclination angles of soft rock. Digital speckle and acoustic emission methods were used as observation tools to explore the combined effects of different soft rock dip angles. The fracture evolution process of the rock mass was analyzed, and the change in mechanical properties of the composite rock mass with angle was studied. The fracture mode of the soft and hard composite rock mass with different inclination angles was obtained. The results show that the deformation and failure of the composite rock mass is a dynamic evolution process in which damage occurs inside the rock mass, with cracks appearing around the soft rock, and extend along and around the soft rock layer, eventually penetrating through the fracture. The deformation and failure process of the combined rock mass is manifested in four stages: original fissure compaction, elastic deformation, plastic deformation and failure. With an increase of the inclination angle of soft rocks, the compaction stage of the rock mass gradually increased, and the elastic modulus gradually decreased. When the inclination angle of soft rock is θ=0° or 15°, the rock mass rupture appears as a combination of soft and hard rock mass failure. When the inclination angle of soft rock is θ=30° or 45°, the rock mass failure mainly occurs in the soft rock area, and the form of rock mass changes from shear failure penetrating the soft rock layer to sliding shear failure along the soft rock layer. The greater the inclination angle of the soft rock layer, the more likely the rock mass is to undergo unstable failure. This study provides a reference for the long-term stability analysis of rock mass engineering containing soft and hard composites and the mechanical behavior of complex layered composite rock mass.