半航空瞬变电磁法在凤凰2号隧道勘察中的应用

Application of Semi-Airborne Transient Electromagnetic Exploration Technology in Fenghuang#2 Tunnel

为解决我国西南地区复杂地形条件下的隧道勘探难题,采用地面激发、空中接收的半航空瞬变电磁法开展试验研究,优化航线设计与数据采集流程、构建基于α-trimmed均值滤波器的天电噪声去除和基于多项式拟合方法的运动噪声去除方法、确定数据叠加方式与时窗积分参数、全域视电阻率计算与探测区域三维成像、隧道充填型岩溶发育区视电阻率特征分析与探测结果综合解释,并通过隧道实际开挖资料对探测结果进行验证。主要结论如下:1)半航空瞬变电磁法能够较准确地推断含水破碎带、岩溶发育区等不良地质结构的范围和深度,能够提前探明隧道地质风险区域并获得地下导电性分布特征,展示了该方法在复杂地形岩溶山区隧道勘察中相较于传统地面物探方法具有地形适应性强、探测效率高等特点;2)通过三维视电阻率成像和关键位置切片结果获得的地质异常区域推断与隧道开挖实际揭露异常吻合度较高,表明该方法可以为隧道岩溶处置预案设计和安全施工提供技术支撑,能够有效避免在隧道施工过程中因隐伏岩溶灾害导致的人员伤亡和财产损失。

An experimental study is performed using the semi-airborne transient electromagnetic method with ground excitation and airborne reception for exploring tunnels under complex terrain conditions in southwest China.Furthermore,the optimization of the route design and data acquisition process is achieved by implementing an airborne transient electromagnetic method,which utilizes aα-trimmed mean filter to remove astroelectric and motion noise based on the polynomial fitting method.Moreover,the data superposition method and time window integration parameters are determined,full domain apparent resistivity is calculated,three-dimensional(3D)imaging of the probing area is achieved,the apparent resistivity of the tunnel-filled karst development area is characterized,and probing results are comprehensively interpreted.The results are validated through field application of the proposed method in the Fenghuan#2 tunnel.The main conclusions obtained from the study are as follows.(1)The semi-airborne transient electromagnetic method can accurately detect the scope and depth of water-bearing fracture zones,karst development zones,and other undesirable geological structures;furthermore,it can detect the geological risk areas of tunnels in advance and acquire the distribution characteristics of underground electrical conductivity,demonstrating stronger terrain adaptability and higher detection efficiency in the tunnel survey of karst mountainous areas compared with the traditional ground-based physical exploration method.(2)The geological anomalies deduced from the 3D visual resistivity imaging and key location slicing outcomes strongly concur with the anomalies exposed through tunnel excavation.Thus,the proposed method has the potential to offer technical support for designing tunnel karst disposal plans to ensure safe construction,which can effectively avoid casualties and property losses due to hidden karst hazards during tunnel construction.