Abstract: The rock strength will decrease under a certain stress, which can lead to different performances in engineering such as the abrupt destroying by strength weakening, long-term strength and so on. So the research on time dependence of rock strength is very important to construction safety and long-term stability of rockmass engineering. Based on the analysis of a large number of test results, evolution characteristics of rock strength and their mechanisms are summarized, and it is can be found that strength weakening of rock is related to the inherent strength of rock, the stress state (yield approach index) and the performing duration of stress. Therefore, time-dependent theoretical model of rock strength is proposed by properly theoretically characterizing the evolutions of cohesion and frictional angle of rock. Simulations to some sets of test data show that the proposed model can perfectly and quantitatively describe the evolution of weakening process of rock strength; moreover, the model is of clear physical concept. The effort of this paper gives a new method to study the time-dependence of rock strength.

Key words: rock strength, time dependence, internal frictional angle, cohesion, yield approach index