A coupled thermal-nonlinear hydraulic-mechanical (THM) model for fault water inrush was carried out in this paper to study the water-rock-temperature interactions and predict the fault water inrush. First, the governing equations of the coupled THM model were established by coupling the particle transport equation, nonlinear flow equation, mechanical equation, and the heat transfer equation. Second, by setting different boundary conditions, the mechanical model, nonlinear hydraulic-mechanical (HM) coupling model, and the thermal-nonlinear hydraulic-mechanical (THM) coupling model were established, respectively. Finally, a numerical simulation of these models was established by using COMSOL Multiphysics. Results indicate that the nonlinear water flow equation could describe the nonlinear water flow process in the fractured zone of the fault. The mining stress and the water velocity had a great influence on the temperature of the fault zone. The temperature change of the fault zone can reflect the change of the seepage field in the fault and confined aquifer. This coupled THM model can provide a numerical simulation method to describe the coupled process of complex geological systems, which can be used to predict the fault water inrush induced by coal mining activities.

Subsurface electromagnetic sensing is used in the mining, tunneling, environmental, groundwater, energy, and geoscience research sectors of the global economy. For underground applications, these methods require focused, compact antenna. We introduce the concept of a ferrite core transmitting coil to time-domain electromagnetic sensing, with an emphasis of forward scanning detection of subsurface hazards from a borehole. First, we develop an analytical expression for mutual coupling between a ferrite core coil transmitting antenna coupled with an air core receiver coil to demonstrate the focusing potential gained by adding a ferrite core. Next, we complete 3-D numerical simulations for a scanning borehole transient electromagnetic (BTEM) device. These simulations include radial scanning and demonstrate the improved resolution achievable with a ferrite core coil transmitting antenna. Finally, a ferrite core coil radial scanning in-hole device was constructed, and field experiments were completed in a shallow borehole. A small high-conductivity object was hidden in the subsurface and then detected with the device within radial plots of subsurface resistivity. Our combined numerical and field experiments present the ferrite core coil antenna as a method for focusing electromagnetic fields with one applicant being hazard prediction ahead of a borehole extended from a tunneling face. We hope these electromagnetic scanning methods find many Earth science and engineering applications.