深埋隧洞爆破开挖损伤区检测及特性研究

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

通过对锦屏二级辅助洞爆破开挖损伤区的检测和数值计算,比较岩体开挖动态过程(包括爆炸荷载和地应力高速释放)及静态过程(地应力重分布)所分别造成的损伤,探明地应力瞬态释放诱发岩体损伤的机制。检测结果表明,地应力的存在对深埋隧洞爆破开挖损伤区具有较大影响。隧洞轴线垂直于最大主应力时的钻爆开挖损伤明显要大于轴线平行于最大主应力时的情况;可以将开挖损伤区分为内损伤区和外损伤区,其中前者主要由爆炸荷载和地应力高速释放二者耦合作用引起,其主要特征是岩体声波速度显著降低;后者主要由应力重分布引起,特征是岩体声波速度缓慢降低。另外,辅助洞实测的岩体内损伤区深度显著大于外损伤区深度,且内损伤区在断面上的分布特性受到开挖二次应力场的影响,表明伴随爆破过程发生的地应力瞬态卸载效应是内损伤区形成的直接原因之一,声波检测检测和数值模拟计算均也证明了这一点。

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.