Abstract The combination of statistic secondary stress field and dynamic disturbance induced by blasting excavation is the major cause of internal damage of rock mass. The static secondary stress field was calculated for a circle tunnel. Then based on the up-layer excavation of city-gate section diversion tunnel of Xiluodu hydropower station,dynamic analysis was conducted. The damage area induced by the combination of static secondary stress field and dynamic disturbance was calculated. During this process,a comparison was made for different material models,based on regression analysis of calculated blasting vibration values and monitored data in field. Result calculated with kinetic-hardening model complies better with the monitored data. As the in-situ stress field increases,the damage area induced by the combination of static and dynamic effect. However,with in-situ stress transient unloading considered,the volume of damaged rock mass is largely increased. Therefore,the transient process of in-situ stress unloading should be considered in blasting excavation of deep underground tunnels. Besides reducing step length or total charge in one delay,prolong the unloading process for in-situ stress is also a measure applicable for controlling rock mass damage.
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