Study on the shear mechanical properties of non-penetrating joints with different apertures and connectivity rates

Investigating the shear mechanical properties of non-penetrating jointed rock masses under various joint characteristics is of significant practical importance for underground engineering construction. This paper combines laboratory direct shear tests and numerical simulation methods to study the macroscopic and microscopic shear mechanical behavior of non-penetrating jointed rock masses under different joint apertures, joint connectivity rates, and normal stresses. A systematic analysis is conducted on the shear stress-shear displacement curves, peak shear strength, normal displacement-shear displacement curves, and stress evolution characteristics. The research findings indicate that: ① The shear stress-shear displacement curves of non-penetrating joints exhibit distinct peaks and generally undergo stages of compaction, crack propagation, post-peak failure, and residual friction. Based on the shapes of shear curves under various conditions, they can be classified into pre-peak ascending and post-peak climbing type (Type Ⅰ), pre-peak ascending and post-peak stepping type (Type Ⅱ), and pre-peak stepping and post-peak climbing type (Type Ⅲ); ② The peak shear strength is negatively correlated with joint aperture and joint connectivity rate, and positively correlated with normal stress. The peak normal displacement is negatively related to joint aperture, and the final normal displacement is negatively related to joint connectivity rate. Both the peak and final normal displacements decrease with the increase of normal stress; ③ Before the intact rock bridge fails to penetrate, stress concentration occurs at the joint ends and crack extension areas. As the joint connectivity rate and joint aperture increase, the degree of stress concentration intensifies. After the rock bridge fails to penetrate and forms a shear plane, stress concentration occurs at the plane, and the stress distribution is mainly influenced by the plane morphology.