Laboratory observation of shear stress recovery in rock joints considering joint compaction and dilatancy

Abstract

Understanding the shear stress recovery mechanism during the stick-slip motion is a fundamental requirement for predicting the sliding behavior of rock joints. In this study, slide-hold-slide (SHS) type direct shear experiments under constant normal stress are performed on granite joints with significant roughness components to investigate the effects of compaction and dilation on the shear stress recovery. The shear stress recovery of rock joints is contributed by the growth of the contact area induced by the compaction during the hold period and the enhancement of dilation work during the re-shear process. The contact area reaches the maximum value under relatively low normal stress after the long hold period. Then, the dilation gradually contributes to the shear stress recovery because the welded asperities or grains are assembled, and the slide needs to ride over these bonded areas. The surface roughness plays a significant role in the shear stress recovery since the initial aperture and asperity morphology affect the compaction and dilation. The greater magnitude of shear stress recovery observed on rougher surfaces can be attributed to the effective normal closure during the hold period and significant dilation after the long hold periods.