Experimental study on the shear creep characteristics of joints under wetting-drying cycles

To better understand the shear creep characteristics of joints under wetting-drying cycles, multi-stage shear creep experiments are firstly conducted on the joints subjected to different wetting-drying cycles. Then, the shear creep damage characteristics of joints are investigated from the microscopic and macroscopic perspectives through wave velocity tests, scanning electron microscope observations, and failure morphologies. The investigation demonstrates that the increasing wetting-drying cycles lead to a porous and disintegrated microstructure of joints, which further results in increases in the shear deformation and steady-creep rate, and decreases in the failure strength and long-term strength. With increasing wetting-drying cycles, the wear rate of joints decreases and the damaged region of joints becomes smaller and invisible. Furthermore, a classification of the shear creep process of joints containing four stages is firstly proposed based on the test results. It is found that the presence of asperities on the rough joints is the physical basis of the existence of strengthening and cutting stages of the shear creep process. Finally, based on the experimental results, a new fractional-order damage creep model of joints considering wetting-drying cycles is proposed.