Water permeability evaluation of fault zone in underground coal mines

Abstract

A large number of mine water inrush data show that a fault zone is often a good water inrush channel. The fault zone internal architecture is very complex. The fault zone exhibits commonly heterogeneous and anisotropic permeability. Water permeability evaluation of fault zones has always been a difficult problem for mine hydrogeologists. This paper presents a semiquantitative permeability evaluation method of mine fault zones based on fault sealing, which evaluates the fault zone overall and partial lateral and vertical water permeabilities. First, a simplified conceptual model of the fault zone is applied to analyze the effects of lithology juxtaposition, fault rock plugging, fracture closure and hydraulic fracturing on groundwater flow. Second, corresponding to the 4 above influence mechanisms, a total of 6 evaluation indexes are obtained, including the juxtaposition probability of aquifers, juxtaposition of aquifers and aquicludes, fault shale content (FSC), aquifer water pressure, plastic deformation index of mudstone, and fault rock plastic deformation index. Finally, the juxtaposition probability of aquifers is used to evaluate the overall lateral permeability, while the juxtaposition of aquifers and aquicludes and FSC are employed to evaluate the partial lateral permeability. The aquifer water pressure is analyzed to evaluate the overall vertical permeability, while the mudstone and fault rock plastic deformation indexes are adopted to evaluate the partial vertical permeability. The overall lateral and vertical permeability grades are high and low, respectively, and the partial lateral and vertical permeability grades include 5 grades ranging from very high to very low. The evaluation method in this paper is applied to evaluate the water permeability of the F1 normal fault in the Nantun coal mine. The F1 fault water permeability evaluation results are consistent with underground exposure and geophysical data, which verifies the feasibility and rationality of this method.