Abstract: Humidity diffusion plays an important role on the deformation of water-sensitive rock in underground engineering. It is not only changed the stress state of rock mass, but also greatly weakened the physico-mechanical properties, which enhanced its time-dependent deformation. By introducing the humidity diffusion in numerical model and establishing the relationship between mechanical response of rock and the humidity diffusion, the numerical model is able to simulate the time-dependent deformation of water-sensitive rock. Numerical simulation of humidity diffusion in tunnel with support system shows that: humidity changes only occur on the surface of tunnel at the beginning of excavation, where the deformation induced by humidity is small but the deformation rate is great. With the humidity further diffusion, the deformation of tunnel increases but the deformation rate decreases, and eventually converges. Numerical simulation represents the stress evolution process of anchors, and the increase of tensile stress in anchors shows its effect on deformation of rock mass. The humidity diffusion reduces the strength of rock and induces rock failure. Failures not only cause the local stress concentration, but also enhance the humidity diffusion in rock mass. It is shown that the humidity diffusion and failures (damage) is an interactive process, namely the humidity-stress-damage coupling.

Key words: humidity diffusion, time-dependent deformation, numerical simulation, humidity-stress-damage coupling