Study on shear mechanical characteristic evolution and influencing factors of rock joint surfaces under cyclic loading conditions

Determining the shear strength of rock joint surfaces is a fundamental problem in the fields of rock mechanics and engineering geology. To obtain the cyclic shear strength of rock joint surfaces under cyclic shearing conditions, an improved formula is proposed. First, cubic splitting tests are used to fabricate joint surfaces and prepare experimental specimens with simulated materials. Second, a series of laboratory cyclic shear tests and data analysis are conducted to investigate the effects of the normal stress, the number of shearing cycles, the rock wall strength, and the surface roughness on the mechanical and morphological properties of the rock joints. The maximum shear strength of the joint surface increases with the normal stress, the rock wall strength, and the joint surface roughness. Considering morphological properties, the normalized values of the indices decrease with the normal stress, the number of shearing cycles, and the joint surface roughness increase, while they increase with increasing rock wall strength. Third, the accuracy of the Adhesive Friction Theory-Barton empirical formula is verified by fitting the experimental data to calculation results. Finally, based on the negative exponential degradation assumption, a new formula is proposed to calculate shear strength under cyclic shear conditions. The proposed calculation method can provide a theoretical reference for improved safety during engineering and design.