深部岩体开挖方式对损伤区影响的试验研究

IN-SITU TEST RESEARCH ON INFLUENCE OF EXCAVATION METHOD ON INDUCED DAMAGE ZONE IN DEEP TUNNEL

深埋隧洞开挖过程中,钻爆法和TBM开挖所对应的不同围岩应力调整路径对开挖损伤区的形成有重要影响,但这一影响尚未引起足够的重视。依托锦屏二级水电站深埋隧洞群的开挖,通过损伤区原位检测试验对比分析2种不同开挖方式下围岩损伤区的特性及形成原因;作为现场试验的补充,在考虑锦屏大理岩基本力学特性和应力瞬态调整效应的基础上,采用数值方法比较应力瞬态和准静态调整所分别形成的开挖损伤区大小。试验结果表明,锦屏二级引水隧洞钻爆开挖的洞段,内损伤区(即严重损伤区)深度可以占到总损伤区深度的50%以上,岩体基本失去承载力。另外,此区域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;而TBM开挖洞段,内损伤区深度约占总损伤区深度的30%,该区域的形成可能更多地受到锦屏大理岩强度时间效应的影响,是表面应力松弛破坏逐渐发展的结果;考虑锦屏大理岩脆-延-塑性转换特性和应力瞬态调整效应后,可以利用数值计算方法较为客观地估计不同开挖应力路径下围岩开挖损伤区的范围。研究结论对深埋隧洞开挖方式选择及支护策略制定具有借鉴意义。

Different stress paths of surrounding rock corresponding to different excavation methods,such as blasting or tunnel boring machine（TBM）,have important influence on the formation of excavation damage zone during construction of deep tunnel.However,the influence has not yet attracted enough attention.Based on the excavation in deep tunnel group of Jinping II hydropower station,the characters and formation factors of damage zones under different excavation methods are discussed by field detecting test;and extents of damage zone induced by in-situ stress transient or quasi-static adjusting are calculated by using numerical simulation method;and the basic mechanical characters of Jinping marble and in-situ stress transient adjusting effect are considered in the calculation.The test results show that the depth of inner damage zone（severely damaged zone） in blasting excavation tunnel accounts for more than 50% of the total damage zone depths;and the rock in this area have been damaged seriously and lost its bearing capacity.The distribution of inner damage zone in the tunnel section is seriously influenced by redistribution stress field,which can be regarded as the evidence of that the in-situ stress transient adjusting effect is one of the direct causes of damage zone formation.In the tunnels excavated by TBM method,the inner damage zone only accounts for 30% of the total damage zone depths;and the formation of this area could be mostly attributed to the time effect of the strength of Jinping marble.It is the result of improvement of stress relaxation at tunnel surface.After considering the mechanical characters of brittle-extension-plastic of marble and transient adjusting effect of in-situ stress,the extents of excavation damage zones under different excavation stress paths can be estimated objectively using numerical simulation method.The conclusion of this paper has important significance for the selection of excavation method and support measures of deep tunnel.