Fig.1 Field investigation site

Fig. 9 and Fig. 10 Transient electromagnetic method inversion result diagrams
The transient electromagnetic method arranges a total of two measurement lines, one is measured in a vertical pipeline and the other is measured along the pipeline. The surface is damp due to leakage of pipe culverts. The buried depth of the pipe is about 10-15m. The pitch is 2m and the transmit current is 40A. It can be seen from Figure 9(a) that there is a low-resistance region between 10m and 15m at a horizontal distance of 10m, which is consistent with the depth of the known culvert position. It can be seen from Figure 9(b) that when the survey line is measured along the culvert, a low-resistance area is presented between 10m-15m deep, reflecting the direction of the underground culvert. (Figure 10) The transient electromagnetic method arranged a total of two measurement lines, both vertical pipeline measurement, the surface dry. The difference is that two different coil sizes are measured, both of which accurately reflect the location of underground culverts (indicated by the red dashed line in the figure).
Case 4: Investigation of leakage of pipe culverts in a project in Hebei Province
The upper part of the area is dominated by modern river alluvium, and the lower part is a dipping alluvium. The terrain is flat and the altitude is between 10m-30m, and the ground slope is less than one thousandth. The eastern plain is a sedimentary area since the Paleozoic era, the upper part is covered with huge sediment, gradually thickening from west to east. The ground surface is flat, the geological conditions are single, mainly farmland, and the groundwater is buried deeply.
If there is leakage in an engineering culvert, the high-density resistivity method and transient electromagnetic method are used to investigate. The transient electromagnetic normal point distance is 1m. On-site drilling sampling can be seen from the figure that the transient electromagnetic method inversion superficial effect is better, and the corresponding drilling sampling is better.

Fig.2 Figure 11 Comparison of transient electromagnetic method and high-density inversion results