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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