Evolution Mechanism Of Damage Induced By Blasting And Excavation Unloading Of Deep Rock Mass And Its Numerical Simulation Methods

Rock excavation of underground tunnels and caverns under high stress is faced with the problem of controlling unloading deformation and cracking damage of rock mass.The dynamic disturbance to rock mass caused by the blasting and the stress transient unloading?excavation transient unloading?of new free surface rock mass are the important causes of underground engineering disasters.Therefore,exploring the evolution mechanism of unloading damage in deep rock mass blasting excavation is an important subject in geotechnical and blasting engineering.In this paper,Dynamic damage of rock mass during blasting excavation of deep rock mass is studied by combining theoretical analysis,experiment and numerical simulation.The following work has been accomplished.Firstly,a simplified one-dimensional mechanical model for transient unloading of rock mass is established.Based on the analytical results of the model,the propagation law of unloading carrier wave in rock mass is analyzed.It is clear that when the unloading rate is high,the reverse tensile stress will occur in the rock mass which is in the compression state.In addition,unloading path,damping and propagation distance have important influence on unloading carrier wave.Simplified load model of coupled action of load and transient unloading of ground stress is established.Secondary stress distribution and dynamic adjustment process of surrounding rock of deep circular tunnel are analyzed,and crack damage distribution of surrounding rock under secondary stress field is calculated.Secondly,the experimental study on the transient unloading effect of rock blasting is carried out to verify the theoretical analysis results.According to the dynamic strain signals collected from the experiment,the unloading process is divided into three main stages:blasting loading,blasting loading unloading and initial stress unloading.Based on the measured data,the attenuation law of rock mass strain rate and strain energy during the unloading process is analyzed.It is clear that in a certain range,the strain rates of the three stages are above 10^-1 s^-1 magnitude,which belongs to high strain rates.Then,the dynamic damage constitutive model of rock considering high stress and high strain rate is established,and the numerical simulation is realized through the UMAT secondary development interface of LS-DYNA.Based on the new material model,the damage evolution process of surrounding rock of deep circular tunnel is simulated,and the damage depth decreases with the increase of unloading duration,and finally tends to the damage depth caused by quasi-static unloading.In the non-uniform stress field,the compression-shear damage zone mainly concentrates in the direction of less in-situ stress,and under certain conditions,radial or circumferential tension crack damage zone will occur on surrounding rock.Finally,the newly developed Peridynamics?PD?method is introduced to simulate the crack propagation process of deep rock mass and the crack damage distribution of surrounding rock caused by blasting and dynamic unloading based on the self-compiled numerical calculation program,which provides a new idea for the research work in related fields.