Simulation research and application on response characteristics of detecting water-filled goaf by transient electromagnetic method

Water inrush disasters poses a great threat to the safe exploitation of coal resources. To solve this problem, the transient electromagnetic method (TEM) was proposed to accurately detect the water accumulation in the goaf. The electromagnetic response characteristics of different water-filled goaves were studied by electromagnetic field theory, numerical simulation and field verification. Through the models of 100% water accumulation, 50% water accumulation, 0% water accumulation, 100% water accumulation with collapsed rock, 50% water accumulation with collapsed rock and 0% water accumulation with collapsed rock goaf, the characteristics of induced voltage attenuation curves were studied. Meanwhile, the relationship between the attenuation voltage value and area of the transmitting coil, the depth of the goaf, the background resistivity, and the delay time were also simulated. The results illustrate that the attenuation curve of induced voltage presented a regular exponential decay form in the 0% water accumulation model but existed abnormal exaltation for voltage in water-filled model. Through the linear fitting curve, it can be seen that the abnormal intensity of the induced voltage becomes stronger as the distance between the measuring point and the center of the target decrement. Moreover, the abnormal amplitude of the induced voltage increases with the rise of the water accumulation and collapsed rock will weakly reduce the low-resistivity anomalous effect on the water-accumulated goaf. In addition, the response value of the attenuation voltage increased as the area of the transmitting coil increases, but decreased with increasing delay time and increasing background resistivity and depth of the target body. The field detection results of the Majiliang coal mine also confirmed the theoretical analysis and the numerical simulation.