Rock Damage Mechanism And Control Due To Excavation Disturbance In Deep Tunnels

The surrounding environment of rock mass was changed caused by the excavation of tunnel,which induced in-situ stress transient unloading on the boundary and resulted the stress concentration in the surrounding rock and caused it damage.The more depth of the cavity is,the more damage caused by in-situ stress transient unloading.In addition,the excavation of tunnels often need a number of blasting delays,which means there is great significance to explore the damage mechanism of repeated blasting and the rock engineering application and safety control.During the excavation of deep tunnels,blasting load and in-situ stress transient unloading are the main influence factor to excavation damage zone(EDZ).In order to explore rock damage extent,the relationship between the peak vibration velocity and damage zone should be established by the combination of numerical simulation and empirical data,which makes the theoretical basis of the full text.Then,the explosive load and the in-situ stress are introduced.The results indicate that,the shorter rise time and the longer total time of blasting load,the deeper damage of the rock.The radial stress and tangential stress induced by the in-situ stress transient unloading have a significant dynamic change process to the final redistribution secondary stress field.The shorter unloading time,the greater dynamic change rate,while the effect of unloading time on tangential stress is much less than radial stress.In addition,the unloading radius also has a greater impact on the unloading effect.The blasting vibration induced by equivalent blasting load and in-situ stress transient unloading are calculated by the combination of numerical simulation and theoretical model,and the damage extents are also compared.The results indicate that,the equivalent blasting load produce tensile stress in the surrounding rock,which caused the damage mechanism of rock is mainly tension or tension-shear failure.The in-situ stress transient unloading mainly produce an compressive stress and it induced the rock compression-shear failure.Every blasting delays has an contribution to the rock EDZ which has an close relationship with the load value and the excavation radius.The MS7 and MS9 blasting delays are the main contributor to the final EDZ which reflects the repeated disturbance.The study also points out that the higher in-situ stress level,the higher influence on the EDZ that caused by in-situ stress transient unloading.Under high in-situ stress level,the transient unloading would be the main factor of rock mass damage.