Experimental investigation on shear behaviors of saw-toothed sandstone joints under various water vapor humidity conditions

Humidity could significantly affect the failure morphology and characteristics of rock joints. This study experimentally investigated the effects of humidity on the mechanical behavior of saw-toothed sandstone joints. Various humidity conditions were created using the chemical thermodynamic vapor–liquid equilibrium principle, which is a non-contact and non-destructive humidity curing method. The rock joints were maintained under these humidity conditions for up to two months, followed by joint shear tests to assess the impact of water vapor on shear performance. The results show that rock joints are relatively more sensitive to humidity under higher normal stress. The second peak shear stress phenomenon occurs in saw-toothed joint samples with large asperity angle. For rock joints under the same normal stress, the greater the humidity the smaller the second peak shear stress. High humidity significantly influences the deformation behavior of sandstone joints by shortening the peak shear displacement and reducing joint dilation. Furthermore, under low and medium humidity, spalling occurs around asperities and cracks are not generated within the body of rock samples. In contrast, for rock joints subjected to high humidity, cracks are generated and extended within the joint body.