高地应力条件下爆破开挖诱发围岩损伤的特性研究

Study of blasting-induced dynamic damage of tunnel surrounding rocks under high in-situ stress

高地应力条件下隧道或硐室钻爆开挖需考虑初始地应力动态卸荷效应,同时其最终损伤形态会受多个因素影响。采用三维有限差分软件FLAC3D讨论了爆破荷载与地应力动态卸荷复合作用下隧道围岩损伤分布,并重点研究了侧压力系数、岩体力学性质、卸荷速率对围岩损伤范围的影响,最后通过赣龙铁路梅花山隧道开挖损伤区检测结果进行了验证。研究表明,考虑动态卸荷效应的围岩损伤范围明显大于只考虑爆破荷载作用下的围岩损伤范围,在中高地应力条件下,初始地应力动态卸荷对围岩的损伤破坏作用不可忽视;随着侧压力系数逐渐增大,损伤区形态呈现明显的方向性,当侧压力系数为1时,损伤区沿开挖轮廓面分布较为均匀,侧压力系数不为1时,损伤区主要向小主应力方向集中;岩石力学性质越好,损伤范围越小;卸荷速率越快,围岩损伤范围越大,但影响并不十分显著。结果可为高地应力下隧道开挖稳定性分析和支护设计提供一定参考。

The dynamic unloading effect should be considered when tunnel or cavern is excavated by drilling and blasting method under high in-situ stress; and its damage zone forms will eventually be affected by multiple factors. By using three-dimensional finite difference software FLAC3D, the distribution of surrounding rock damage zone induced by the coupling effect of blasting load and dynamic unloading is discussed; then the influences of lateral pressure coefficient, the mechanical properties of rock mass and the unloading rate on damage range of surrounding rock are taken into account in the analyses; and finally through the excavation damage zone detection data of Meihuashan Tunnel of Gan-Long Railway in Jiangxi province. The results of numerical simulation are verified. Researches show that the rock damage zone under the coupling effect of blasting load and dynamic unloading is significantly greater than that only considering the blasting load; dynamic unloading of in-situ stress can not be ignored. As the lateral pressure coefficient increases gradually, the damaged zone presents the obvious directivity, when the lateral pressure coefficient is 1, the damaged zone will uniformly distributed along the excavation contour surface, and when the lateral pressure coefficient is not 1, the damage zone will mainly concentrate in minimum principal stress direction. The better rock mechanical properties is, the smaller the damage zone will be. The faster the unloading rate, the larger the damage zone of surrounding rock will be; but the impact is not significant. The results provide suggestions for stability analysis of tunnels under high in-situ stress and supporting design of the cracked surrounding rock.