Distinct Element Simulation For Ejection Of Rockburst Under Conditions Of Excavation Unloading And Dynamic Disturbance

As ejection rockburst disasters caused by excavation unloading and dynamic disturbance loads of underground rock mass under high geo-stress conditions are getting more frequent and destructive, and a high stress state of rocks due to the excavation unloading process adds to the instability of surrounding rocks which results in sudden rockburst and ejection towards the excavation free face under the influence of disturbance loads, both the stability of surrounding rocks and the safety of personnel are threatened.This paper studies the numerical simulation of ejection rockburst process under conditions of excavation unloading and dynamic disturbance loads with the discrete element method. This is a further development to UDEC, the software for discrete element method simulation. Intact rocks are divided into small units and those elements together with the contact surfaces in between them serve as our study model. A degraded contact surface together with other parameters such as ejection speed of the burst rocks and kinetic energy make up the basis of precise simulation of the rockburst process under the combined effect of excavation unloading and dynamic disturbance loads with the discrete element method. In this way, simulation of discontinuous deformation analysis of ejection rockburst becomes reality which would have been impossible with the continuous-media-based traditional numerical simulation method, and thus providing a powerful solution to rockburst study and forecast under the combined effect of evacuation unloading and dynamic disturbance. With the discrete element method, this paper studies energy evolvement during the rockburst process caused by evacuation unloading and dynamic disturbance. Results show that the energy of ejection rockburst derives from the superposition of accumulated elastic strain energy in the rock mass itself caused by evacuation unloading and the energy that comes from dynamic disturbance loads. Rockburst is more violent under the combined effect of evacuation unloading and dynamic disturbance loads compared with the sole cause of evacuation unloading. In addition, with the discrete element method simulation, influence factors to rockburst are analyzed. For the practice of rockburst forecast, aside from the magnitude of stress field of the original site, direction and deviator stress of the original stress filed is also taken into consideration. Under the conditions of high geo-stress field and dynamic disturbance loads caused by engineering blasting, rockburst is likely to occur to intact and solid Type1～Ⅲ rocks during tunnel evacuation unloading. Normal shotcrete and rock bolt support cannot provide enough protection to prevent rockburst from happening, but it can reduce the breaking strength of rockburst and ejection speed, which lower the destructiveness of rockburst.