Shear stress relaxation behavior of rock discontinuities with different joint roughness coefficient and stress histories

Abstract

Abstract Stress relaxation is an important time-dependent behavior of rock mass. To investigate the stress relaxation behavior and the influence of stress history and surface morphology on the stress relaxation of rock discontinuity, iso-stress cyclic relaxation tests and shear stress relaxation tests with loading–unloading stress histories were conducted on artificial rock discontinuity samples and natural rock discontinuity samples. The characteristics of the stress relaxation curve with different stress histories were investigated in detail, and the relationship between the accumulated plastic deformation and relaxation stress was established. Results revealed that the stress history caused the weakening of the stress relaxation ability. The greater the joint roughness coefficient (JRC), the more noticeable is the stress relaxation. Moreover, the stress history presents a greater effect on stress relaxation as the JRC increases. The stress relaxation exhibits a linear relationship with the plastic deformation that occurred before the stress relaxation. It demonstrates that the relaxation stress and plastic deformation are homogenous and that the elastic energy is the power of stress relaxation. The roughness or asperities of rock discontinuity provides the “space” for the stress relaxation.