Mechanical properties of soft-hard interbedded rock mass with different damage degrees under cyclic loading-unloading and drying-wetting cycles

Exploring the mechanical properties of soft-hard interbedded rock mass with different initial damages is crucial for assessing the stability of post-seismic damaged rock masses under cyclic drying and wetting conditions. Taking the interbedded rock mass of metasandstone and phyllite as a research object, the samples with different initial damage degrees were prepared through cyclic loading and unloading tests followed by cyclic drying and wetting tests. Subsequently, uniaxial compression tests were conducted to investigate the deformation and failure characteristics, crack evolution process, and strength degradation laws of samples with different initial damage degrees, to explore the precursor information of sample failure, and to reveal the damage degradation mechanism from a micro perspective. The results indicate that the deformation difference coefficient can quantify the discrepancies in deformation across different areas of the sample surface. The propagation of transcrystalline cracks and intercrystalline cracks extends throughout the loading process, with tensile fracturing being the primary mode of failure. The increase in the proportion of shear fractures will cause an increase in the coefficient of variation (C_v) of the RA/AF values. When the C_v reaches 6.5, the sample is approaching failure. The shear failure mode of the sample is primarily governed by the structural features of the rock mass, while initial damage influences the type of failure and the development of cracks. Initial damage leads to a decrease in elastic modulus, compressive strength, and failure displacement. The increase in microcracks and the weakening of interparticle bonding are the fundamental causes of the deterioration of the rock mass' s macroscopic mechanical properties.