Numerical Simulation and Application of Time-lapse Resistivity Method in the Fracture Zone in a Red Soil Layer Under Mining Influence

Shallow coal seam mining activities in northern Shaanxi can damage the water-blocking capacity of the massive red soil layer of the Baode Formation, severely damaging the ecological environment. Monitoring the extent of damage to the red soil layer using the time-lapse resistivity method can provide crucial technical support for water-conserving coal mining. This study enhances the resolution capability of the resistivity method for deep fractures in the red soil layer by introducing a time-lapse inversion method under spatiotemporal constraints. Numerical simulation results indicate that, compared to traditional smooth constraint time-lapse inversion, the proposed spatial-temporal constraint time-lapse inversion can more clearly reconstruct the morphological characteristics of the fracture zone. This is especially true for fracture zones with lower development heights, where spatial-temporal constrained time-lapse inversion demonstrates stronger resolution capabilities. The method was subsequently applied to monitor mining activities in the Shenfu mining area. Actual measurements revealed that the fracture zone developed up to an elevation of 1200 m without completely penetrating the red soil layer. In some areas fractures extended to the surface, and their positions corresponded well with the simulation results.