Dynamic Failure Mechanism Of Deep Surrounding Rock Considering Energy Release Velocity

Excavation of deep rock is often involved in hydropower projects,mining of mineral resources and underground protection projects et al.Environment of the original rock mass is changed,which resulting in dynamic adjustment of strain energy and a series of engineering geological disasters,such as vibration,damage,rock bursts,the dynamic adjustment effect of rock mass is more significant in the conditions of high in-situ stress.Therefore,the exploration on the changing process of stress and energy field is of great significance to engineering application and safety control.The excavation process of deep rock mass is complex.In this paper,the stress field under instantaneous stress unloading is obtained by using semi-infinite rod model and spherical cavity model;by analyzing the mechanical process of deep tunnel excavation,it is considered that the stress and energy in deep tunnel excavation is a transient release process.Based on the consistency of mechanical mechanism between projectile-target punching and deep tunnel excavation,a punching model is established to further analyze the mechanical response of rock mass from the perspective of plane stress;based on the insufficiency of energy release rate index,the index of energy release velocity is put forward,and the corresponding energy failure criterion is established,which can be extended to the field of civil engineering;the conditions and criteria of rock burst are analyzed,and point out the shortcomings of existing criteria,the rationality of energy release velocity in evaluating failure tendency of surrounding rock is analyzed from physical mechanismFor the semi-infinite rod model,the dynamic and static stresses caused by rectangular loads are equal,there will be no peak stress or tensile stress,while for the spherical cavity model,the peak tension stress will appear at the moment of unloading.Through numerical simulation,the dynamic stress field of the target is obtained.The radial stress increases first and then decreases,while the tangential stress decreases first and then increases;The difference of direction and numerical value between the radial stress and the tangential stress leads to the peak deviating stress,which resulting in the failure of the material;With the shortening of unloading time,the varying effect of dynamic stress is more obvious,and the change rate of dynamic stress is larger;under the same unloading time,the change rate of radial stress is greater than that of tangential stress.It can be seen from the energy variation curve that under the condition of rapid stress unloading,the strain energy decreases first and then increases and generate dynamic fluctuation,the peak value appears in the process of fluctuation.The direction of energy transfer is opposite to that of unloading stress wave,energy transfers from the outer boundary to the punching surface,which leads to the accumulation of strain energy,the closer to the punching surface,the more obvious the accumulation of strain energy is.With the shortening of the unloading time,the accumulation degree of strain energy are higher.The critical depth of rock burst is evaluated by energy failure criterion,and the following conclusions are drawn: unloading time is closely related to critical depth,and the critical depth range increases by 4.8%～11.9%.Finally,the construction method of controlling energy release effect is put forward.