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.

Under cyclic load conditions, rock mass engineering such as tunnels and underground storage is prone to large deformation and collapse due to the gradual deterioration of surrounding rock performance. It is of great significance to study the shear characteristics of rock joints and macro-mesoscopic mechanism for evaluating the service safety of rock mass engineering under cyclic load conditions. Joint specimens were prepared with high strength gypsum, cyclic shear tests were carried out under constant normal load, and the numerical simulation method of finite element and discrete element coupling was used. The results show that the greater the roughness of joint surface, the greater the peak shear strength. In the same number of cycles, the peak shear strength decreases with the increase of cyclic shear displacement. The average dilatancy angle decreases with the increase of the number of cycles. In the same number of cycles, the average dilatancy angle decreases with the increase of cyclic shear displacement and increases with the increase of joint roughness. With the progress of cyclic shear, the stress evolution tends to be stable, and the number of cracks decreases with the increase of cyclic shear cycles.

The structural characteristics of nanopores are known to significantly affect the wetting effect in coal seam water injection. Currently, the three-dimensional characterization of nanopores in coal relies mainly on digital images, whereas poor image resolution and segmentation methods pose significant challenges. Therefore, using coal samples from Wudong Coal Mine in China as an example, cryo-focused ion beam scanning electron microscopy (cryo-FIB-SEM) and deep learning segmentation methods were implemented to accurately characterize the nanopores and water distribution. In the obtained pore structure, the number of isolated pores was higher than that of connected pores, while the volume of connected pores was significantly larger than that of isolated pores, comprising the key path and storage space for external water to enter the coal body. The water content of isolated pores mainly depends on the permeability of the coal matrix. The connectivity of single pores can be characterized by the coordination number, whose increase leads to the number of pores exponentially decreasing. The connectivity of pore clusters depends on the number of internal branches. The number of branches in the pore cluster increases exponentially with the increasing total length, total volume and average radius of the cluster, and the connectivity is correspondingly enhanced. The increase in pore size enhances the shape factor, surface area and connectivity of pores while reducing tortuosity, which in turn facilitates coal wetting. The accurate characterization of coal nanopores in this study helps to scientifically evaluate the effect of coal seam water injection, highlighting the importance of increased pore size and improved pore connectivity for enhanced water injection effectiveness.