高密度电法与音频大地电磁法在城市输水隧洞勘察中的应用

Application of Multi-electrode Resistivity Method and Audio-frequency Magnetotelluric Method in the Investigation of Urban Water Tunnel

为避免在建造浙江省某大型输水隧洞时发生地质灾害,通过高密度电法与音频大地电磁法相结合以查明浅部覆盖层厚度、基岩风化厚度及断裂破碎带构造。采用高密度电法探测浅层地下含水裂隙带的异常形态及岩体的稳定性,部分区域通过音频大地电磁法推断出深部地质断裂构造位置。依据前期地质资料,建立了相应地电模型,通过对模型响应数据进行反演试算,发现这两种方法相结合具有可行性,能精确反映地下不同深度的地质情况,探测结果能为后期设计和施工提供参考依据。实测数据反演结果显示:地层上部杂填土、含砾粉质黏土、碎石夹黏土等厚1~15 m;高密度电法识别出6条断裂发育带的位置,倾角为56°~75°,影响宽度为10~15 m;音频大地电磁法识别出一处断裂发育带,影响宽度约为15 m;裂隙发育带、构造破碎带对岩体完整性破坏较大,强度受软弱结构面控制,易受地下水作用影响,浅部岩体稳定性较差,电阻率表现为低阻特征并向下延伸。

To avoid geological hazards during the construction of a large water tunnel in Zhejiang province,an audio-frequency magnetotelluric(AMT)method in combination with multi-electrode resistivity method was used to investigate shallow overburden thickness,bedrock weathering thickness,and fault structures.The abnormal shape of shallow underground water-bearing fracture zones and rock mass stability were revealed by multi-electrode resistivity method.The locations of deep geological faults were inferred by AMT in some areas.The geoelectrical models were established based on the previous geological data.The inversion results demonstrate that the combination of two methods can accurately indicate the responses of underground geological bodies with different depths.The simulation results also provide a reference for design and construction of the future investigation.The inversion results of field data show that the thickness of miscellaneous fill,conglomeratic silty clay,and gravel clay,is 1-15 m;the cross profiles of multi-electrode resistivity inversion reveal 6 fracture(joint)development zones,the dip angles are 56°-75°,the widths are 10-15 m;AMT inversion indicates a concealed developed fault area with the width of^15 m;structural fracture zones have great damages on the stability of rock mass in this area,which is controlled by the weak structural plane,and easily affected by groundwater;the stability of rock mass is poorer in the shallow location of AMT profile,which is manifested as a downward extended low resistivity anomaly.