DETECTING AND STUDY OF BLASTING EXCAVATION-INDUCED DAMAGE OF DEEP TUNNEL AND ITS CHARACTERS

Through detecting and numerical simulation of the blasting excavation-induced damage zone(BEDZ) in Jinping II service tunnel,the damage zones induced by dynamic excavation process including blasting load and in-situ stress transient unloading and static excavation process(redistribution of in-situ stress) respectively are compared and discussed. Damage mechanism of in-situ stress transient unloading to rock mass is also studied using numerical simulation technique. The result indicates that the depth of BEDZ is determined by the existence of in-situ stress. When the direction of tunnel axis is vertical to the maximum principal stress,the depth of BEDZ is larger than that of which the direction of tunnel axis is parallel to the maximum principal stress. The BEDZ of Jinping II service tunnel could be divided into two parts:inner damage zone(IDZ) and outer damage zone(ODZ). The IDZ is mainly induced by the coupling effect of blasting loading and transient unloading of geostress,and it is characterized by a sharp reduction of acoustic velocity of rock mass;while the ODZ is caused by redistribution of in-situ stress and characterized by a gradual reduction of acoustic velocity. In addition,the monitored depth of IDZ in Jinping II service tunnel is significantly larger than that of ODZ,and its distribution on tunnel section is strongly controlled by redistribution stress field after excavation. It is indicated that the effect of in-situ stress transient unloading during blasting is one of the direct causes of the formation of IDZ,which is confirmed by both detecting results and theoretical analysis.