Research on groundwater seepage through fault zones in coal mines

Water inrush in coal mines is commonly linked to fault zones. Excavation of the coal seam can lead to new fractures in the associated fault zone. Many water inrush disasters have a time lag, which is closely related to the fault zone’s permeability. In the present study, three kinds of fault analog samples (artificially reproduced samples analogous to the fault material) are prepared according to microscopic characteristics of natural fault samples, and permeability tests are carried out under constant water pressure. By monitoring the pressure change during the permeability test, the seepage process in the fault zone can be divided into three stages: slow growth, rapid growth, and saturation. In addition, a time-dependent equation of porosity and permeability in porous media is introduced in the coefficient partial differential equation module in COMSOL Multiphysics. By fully coupling with the Brinkman flow module, three kinds of numerical models of the fault zone with different initial porosity and permeability are established. The porosity growth rates in the three fault-zone seepage stages are 24, 23, and 2%, respectively. The growth rates of permeability are 122, 110, and 8%, respectively. The growth rates of flow velocity are 211, 185, and 11%, respectively. The growth rate of the fault model with low porosity and low permeability is lower than that of the other two models. By discussing different conceptual models of water inrush from faults, the results indicate that water inrush disasters can be delayed or prevented if the clay content in the fault is high.