基于高频大地电磁法对三峡某隧道不良地质体的勘察

Exploration of Bad Geological Body in a Three Gorges Tunnel Based on High Frequency Magnetotelluric Method

拟建隧道地表溶蚀风化严重、节理裂隙较发育,断层、岩溶及其赋水性是该隧道施工的隐患,本文将高频大地电磁法应用于该隧道路肩线所经过的基岩内的岩溶及断裂发育带的勘察,观测频率为0.001~100kHz的天然场源,根据勘察的视电阻率异常区和反演结果,结合工程钻探及地质资料,圈定了隐伏的岩溶和断裂发育带,根据隧道开挖的资料统计,所揭露的溶洞发育带与解释的低阻异常相对应,说明高频大地电磁法是一种勘探深度大、勘探效果好的隧道岩溶裂隙发育带勘探方法,其结果可以指导隧道开挖过程中的地质灾害的预防和处理。

The severely weathered dissolution,joint fissures,faults,water-bearing rock are the hidden danger in the tunnel excavation.In this paper,high-frequency magnetotelluric method is used in the exploration of the karst caves and fault developed belts of these tunnels.We adopted the high frequency magnetotelluric method（HMT） in the frequencies ranging from 0.001 to 100 kHz by using the natural electromagnetic source.The position and size of karst caves and fault developed belts are deployed according to apparent resistivity anomalies,inversion results of HMT,engineering drilling and geological data.It shows that all the large-scale karst caves are in the area which represents low resistivity anomalies on the basis of data statistics.It shows that HMT can be used in the deep karst exploration and that it is available for the investigation of karst-fractured zone.In hence,it can be used to prevent and deal with the geological disaster in the tunnel excavation.