等值反磁通瞬变电磁法在城市浅层空洞探测中的应用

    Application of the opposing-coils transient electromagnetic method in detection of urban shallow cavities

    • 摘要: 快速高效地查明城市中引起地面塌陷的隐患,对于城市建设、灾害防护及保护人民财产具有重要意义。将城市浅层地面塌陷归纳为3类:溶蚀作用造成的空洞塌陷、无序抽排地下水造成的土洞塌陷以及人防工程老旧空洞塌陷,通过正演计算,研究分析了3类空洞地质模型的等值反磁通瞬变电磁响应规律,以及各模型分别在高阻和低阻覆盖层下的衰减曲线的变化特征;利用岩石的瞬变电磁响应变化率分析了各类空洞地质模型的电性特征。正演结果表明:溶蚀空洞模型和土洞模型与围岩相比呈低阻特性,人防空洞模型呈高阻特性;3种模型的瞬变电磁响应变化率表明等值反磁通技术对各类空洞隐患均具有较好的识别能力。将等值反磁通瞬变电磁法应用于昆明、郑州等地的3类空洞探测,结果证明该方法对城市浅部空洞探测是行之有效的。

       

      Abstract: Quickly and efficiently identifying the hidden dangers inducing ground collapse in cities are greatly significant for urban construction, disaster protection, and protection of people's properties. In this study, the urban shallow ground collapse was classified into cavities caused by dissolution, disorderly drainage of groundwater, and old civil air defense works. Through forward calculations, this study analyzed the response laws of the geological models of the three types of cavities using the opposing-coils transient electromagnetic method (OCTEM), as well as the various characteristics of attenuation curves of the models under high resistance and low resistance overburden strata. Moreover, this study investigated the electrical characteristics of the geological models of the three types of cavities using the rate of change in the transient electromagnetic responses of rocks. The forward results are as follows. Compared with the surrounding rocks, both the models of cavities caused by dissolution and disorderly drainage of groundwater showed low resistance characteristics, while the model of cavities caused by civil air defense works showed high resistance characteristics. The rates of change in the transient electromagnetic responses of the three models show that the opposing-coils technology has a good ability to identify the hidden dangers inducing all kinds of cavities. The application results of the OCTEM to the detection of three types of cavities in areas such as Kunming and Zhengzhou show that this method is effective for the detection of urban shallow cavities.

       

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