Numerical Simulation Of Deformation-cracking Processes Of The Chamber Surrounding Rock Under Hydrostatic Pressure And Impact

To extend features of the developed continuum-discontinuum method,we introduced the Ⅱ-type fracture energy in the method where Ⅰ-type fracture energy was introduced.The method is a combined Lagrangian-discrete element method.In order to observe more intuitively the process of crack initiation and propagation in the model,the function of stress nephogram display and preservation with cracks is added.Numerical modeling of the elastic,hardening,meta-instable,instable and residual stages of the rock specimen in direct shear was conducted.The present method was verified through a comparison of the used Ⅱ-type fracture energy in calculation and the obtained Ⅱ-type fracture energy.The following results were found: The relation between the averaged shear stress acting at the upper end of the rock specimen and the number of timesteps can be divided into four stages: elastic stage,hardening stage,softening stage(including meta-instable stage and instable stage)and residual deformational stage;at the meta-instable stage,the final hindrance from cracking is destroyed,after which the fault surface completely enters the softening status,leading to inevitable fault instability.Effects of the excavation unloading time and chamber diameter on the deformation and cracking processes of the chamber surrounding rock under hydrostatic pressure were studied numerically.The following results were obtained: With an increase of the number of timesteps,several shear cracks extend toward the depth of the surrounding rock,and a few cracks cross each other to form V-shaped notches;eventually,the surrounding rock is in equilibrium state or not;with a decrease of the chamber diameter,the number of shear crack segments decreases,the maximum depth of V-shaped notches decreases,and the number of approximately parallel shear cracks also decreases;for a small chamber,the surrounding rock easily reaches an equilibrium state;effects of the excavation unloading time on the cracking process exhibit a certain regularities and complexities to some extent.The numerical simulation of the deformation-cracking-collapse process of chamber surrounding rock under the action of half sinusoidal waves is carried out.The mechanism of cracking of chamber surrounding rock caused by stress wave reflection and superposition is expounded on focus.In addition,the influence of the impact load amplitude is also discussed.With the decrease of the impact load amplitude,the number and distribution range of tensile and shear cracks decrease,and the maximum depth of V-shaped notches decreases.