Strength degradation of argillaceous sandstone induced by relaxation behaviour

The underground engineering time-dependent stability is affected by the surrounding rock combination behaviors of creep and relaxation. A series of triaxial relaxation tests under 10-30 MPa confining pressure was conducted on argillaceous sandstone to investigate the relaxation-induced strength degradation. Based on tested data, an empirical equation is proposed to describe the rock strength degradation quantitatively. The rock strength after relaxation is approximately 67-83 % of the instant strength. While the rock strength after the creep process is only about 40 similar to 60 % of its instant strength, the results indicate the rock strength degradation induced by relaxation is much lower than that of creep behavior.