穿越花岗岩蚀变带隧道的工程地质特征及突涌机理分析

Mechanics Analysis of Inrush and Characteristic of Engineering Geology for Tunnels Passing Through Altered Granite Zone

埋深175 m的灯火寨隧道发生多次大规模的突泥、涌水事故。区域地质调查发现灯火寨隧道的突涌灾害发生在晶洞花岗岩与凝灰岩的接触带,在接触带附近两者均发生大规模蚀变。岩相学的试验揭示逐渐靠近接触带晶洞花岗岩依次发育钠长石化、绢云母化和高岭土化蚀变;凝灰岩依次发育硅化和蒙脱石化蚀变。孔隙度、饱和含水量和单轴抗压强度等试验揭示蚀变导致岩体的物理力学性能显著劣化(硅化凝灰岩除外)。尤其是接触带中心发育的带状高岭土化粘土和蒙脱石化粘土。水理试验揭示蚀变粘土的呈现高膨胀性、易崩解、易泥化等不良工程性质。正是由于深埋、带状蚀变粘土的存在,隧道的开挖扰动、应力重分布和地下水排泄等耦合作用才触发多次大规模泥石流状的突涌和通达地表的坍陷。

Several large-scale mud and water inrush events occurred during excavation of the Denghuazhai Tunnel at a depth of 175 m.It was revealed The inrush hazards occurred in the contact zone between geodetic granite and tuff by regional geological investigation.Large-scale alteration occurred both in geodetic granite and tuff near the contact zone.Petrographic and mineralogical tests indicated that albitized,sericitized and kaolinized alteration occurred in geodetic granite,and siliconized and montmorillonitized alteration were developed in tuff gradually towards the contact zone.Tests on porosity,saturated water content and uniaxial compressive strength indicated that alteration led to significant deterioration of physical and mechanical properties of rock masses(except for siliconized tuff).Especially,for the zonal kaolinized and montmorillonitized clay in the central area of contact zone,the physical and mechanical properties were poor and obvious swelling,disintegration and argillaton were observed.Hdrophysical tests indicated that the altered clay exhibited remarkably proneness to swelling,disintegration and argillation.Due to the existence of deeply-buried zonal altered clay,a few large-scale inrush events similar to debris flow and surface collapses were triggered by the coupled effects of excavation disturbance,stress redistribution and groundwater drainage.