Numerical Analysis On Damage Evolution And Time-dependent Failure Of Rock With Interlayer Surrounding Underground Tunnel

Based on the knowledge of longtime strength of rocks, the strength degradation equation is employed in the representative volume element to study damage evolution and time-dependent failure of rock surrounding underground tunnel, by applying a numerical simulation method based on RFPA, in view of physical and mechanical properties of rock, strength and elasticity modulus etc., are degraded and mesoscopic damage accumulation with time due to the influence of environmental variation.Firstly, creep tests of rock under uniaxial compression and time-dependent deformation process of tunnel are simulated. And compared with the results of physical tests, simulation result well reflects three typical stages of rock creep:the initial creep, steady creep and accelerated creep; time-dependent deformation curves of roof, floor and walls from numerical simulation of tunnel were generally consistent with those from physical model tests. As a parameter analysis case, the impact of lateral pressure coefficient on time-dependent deformation and failure characteristics of tunnel also is simulated. The results show the wall-to-wall closure displacement of tunnel increases gradually with increase of lateral pressure coefficient, while roof-to-floor convergence displacement decreases gradually. And local mesoscopic damage evolution and macroscopical time-dependent failure of tunnel surrounding rock also are explained.Secondly, damage evolution and time-dependent failure of rock surrounding underground tunnel under different weak interbed distribution are simulated. Symmetric distribution of stress field and displacement field of rock surrounding underground tunnel under the influence of weak interlayer occurs obvious change, the phenomenon of "migration" near to the weak interlayer, which makes stress concentration formed between tunnel and weak interlayer and then causes displacement and failure of the rock mass near weak interlayer to increase. And because of the difference of weak interlayer distribution location, time-dependent failure processes of tunnel have obvious differences. As a parameter analysis case, the impact of lateral pressure coefficient on time-dependent deformation and failure characteristics of tunnel also is simulated. The results show roof and walls displacement of tunnel increase gradually with increase of thickness of weak interlayer and failure of tunnel becomes more and more serious, the effect of thickness on time-dependent failure of tunnel increases significantly.Then, damage evolution and time-dependent failure of rock surrounding underground tunnel in jointed rock mass with different angles are simulated. Distribution rule of stress field of rock surrounding underground tunnel under the influence of weak interlayer is obviously changed. If the joint angle is 0°, tunnel is given priority to wall caving on both sides. With the change of joint angle, time-dependent damage failure of rock-surrounding underground tunnel is also changed obviously, and damage failure zone rotates with the increase of joint angle correspondingly. If the joint direction is vertical, the failure of tunnel focuses on the floor and the vault, with the serious phenomenon of roof caving and floor heave. Meanwhile, displacements of tunnel are obviously changed, and displacements of tunnel presents the general trend of increase after decrease first with the increase of joint angle.Last, as an example analysis, damage evolution and time-dependent failure of rock surrounding underground Taloun service tunnel in Iran are simulated.