Abstract:
Mine water inrush poses a serious threat to the safe production of coal mines in China. The
transient electromagnetic method (TEM) on the ground has been applied to explore water-bearing structures,
but the resolution is low. Therefore, some geophysicists in China moved the TEM onto underground
coal mine roadways and obtained good results at the end of the last century. Although the TEM has
been applied in mining for many years, there are so few theoretical studies that the data interpretation
is not accurate. It is necessary to study the transient electromagnetic eld diffusion in the entire space
with physical or numerical simulation methods. First, based on the diffusion equations, we deduced the
wave number domain equations, whose whole-space electromagnetic eld is excited by a 3-D source in a
2-D geoelectric model; then, we derived the 2.5-D nite-difference time domain equations. At the beginning
of the calculation, we gave the grid nodes near the source the initial values with the cosine ltering method.
To improve the calculating ef ciency, the time intervals gradually increased with time. At the end of the
calculation, we transformed the calculating results from the wave number domain to the space domain by
tting the segmented exponential function. Compared with the analytical solutions, the numerical solutions
are accurate, and the algorithm is reliable and ef cient. The simulation results of a collapse-column model
show that the transient electromagnetic eld diffusion in the entire space is dominated by low-resistivity
bodies.
