Abstract: Brittle failure is usually observed during excavation of surrounding rock, while the simulation results of brittle failure often vary with numerical methods. Therefore, it is highly important to study the applicability of different numerical methods to simulate brittle failure characteristics of surrounding rock. Firstly, in the continuous method, the calculation formula of residual stress in the improved stress drop model is deduced, which removes the correlation of the change of strength parameters in the traditional stress drop model, and is verified by simulated uniaxial compression test. Then, the continuum method (method 1) and the continuum-discontinuum method (method 2) were used to simulate brittle failure characteristics of circular tunnel surrounding rock under hydrostatic pressure. Finally, taking Taipingyi tunnel as an application example, two methods were used to simulate brittle failure characteristics of circular tunnel surrounding rock under non-hydrostatic pressure. It is found that under hydrostatic pressure, the results obtained by both methods are similar to those obtained by the field observation or laboratory experiments, while the failure zones obtained by method 1 is larger. Under non-hydrostatic pressure, although the result obtained by method 1 is similar to that obtained by field observation of surrounding rock failure of the Taipingyi tunnel, the results obtained by method 2 are closer to that by the field observation. This phenomenon could be explained as follows. In method 1, the surrounding rock is still a continuous after failure, which is conducive to stress transfer between rock blocks, thus facilitating the development of failure zones; while in method 2, the surrounding rock is converted into a discontinuum after cracking, and the contact and friction forces reflect the interaction between rock blocks and consume the system energy, thus limiting the development of cracking zones.

Key words: brittle failure, stress drop, continuum method, continuum-discontinuum method, contact force, friction force