###### Abstract  
Mine floods caused by water-bearing collapse columns are one of the most significant types of coal mine disasters in advanced detection. The transient electromagnetic method (TEM), one of the most effective means, can detect the collapse column in coal mines. However, the research on TEM used on the ground is mainly limited to half-space that does not follow underground mining conditions. This research used the whole-space TEM to detect the water-bearing collapse columns in front of the roadway. Based on the time-domain finite element method (TDFEM) and actual coal-measure strata data, this paper built the whole-space geo-electric models, summarized response characteristics, and proposed \"geometric gravity center\" effect. The results showed that the simulation based on TDFEM could accurately reflect the TEM response law, and the advanced detection using TEM in a mine environment was consistent with the actual situation. t 20221213  
the transient electromagnetic response of water-bearing columns can not only provide a theoretical foundation for its three-dimensional inversion and data interpretation, but it can also encourage the development and use of this method, which is of great practical significance for the prevention and control of water in coal mines and safe production. The transient electromagnetic method used in mine hydrogeological exploration is mainly divided into the ground and underground [16; 17; 18; 19]. Affected by the narrow space of the underground tunnel, the detection devices used on the ground are different from those used underground. As shown in Figure 1, the equipment on the floor is a large ring with varying lengths of side from tens of meters to hundreds of meters, while the underground equipment is small with a side length below 3 m. In addition, the geological anomalies to be detected are underground, so the TEM used on the ground has the characteristics of a half-space response. As shown in Figure 2, the reaction of underground TEM will be affected by the whole space. Unfortunately, most current studies on transient electromagnetic detection are concentrated in the half-space. With the increase of mining depth, the distance between the ground detection device and the detection target will also increase, resulting in a decrease in the resolution of ground detection. Therefore, it is significant to study the whole space as the research object of the underground TEM data processing method. The transient electromagnetic forward method is an effective way to study the transient electromagnetic response, mainly including the time-domain finite-difference (TDFD) method, the finite volume method, the integral equation method, and the finite element method (FEM) [20; 21; 22; 23]. Compared with the above methods, the main advantages of the finite element method are its discrete spatial flexibility and high simulation accuracy for complex geometries [24]. In addition, with the rapid development of computer hardware, the problem of extensive computing time and memory requirements has been effectively alleviated, so the FEM is considered a common method. [PERSON] and [PERSON] [25] used the FEM to simulate the TEM response of low resistivity ore bodies and discovered that the three-dimensional numerical simulation is essentially comparable with the field measured results, demonstrating the viability of the approach. Since then, [PERSON] et al. [26] also carried out exploratory research on the finite element method for solving the forward problem of three-dimensional transient electromagnetic method. [PERSON] [27] performed three-dimensional forward of the loop source transient electromagnetic approach based  
Figure 1: Ground TEM. Figure 2: Underground TEM. on the concept of separating the anomalous field and the background field. Through the TDFEM and tetrahedral mesh, [PERSON] et al. studied the impact of terrain on the transient electromagnetic response [28]. [PERSON] et al.