Abstract
Hydraulic conductivity is an important parameter for predicting groundwater inrush in coal mining worksites. Hydraulic conductivity varies with deformation and failure of rocks induced by mining. Understanding the evolution pattern of hydraulic conductivity during mining is important for accurately predicting groundwater inrush. In this study, variations of hydraulic conductivity of rock samples during rock deformation and failure were measured using the triaxial servo rock mechanic test in a laboratory. The exponential formula of hydraulic conductivity-volume strain was proposed based on the experimental data. The finite-difference numerical model FLAC3D was modified by replacing constant hydraulic conductivity with the strain-dependent hydraulic conductivity. The coupled water flow and rock deformation and failure were simulated using the modified model. The results indicate that in the early time, the rocks undergo elastic compression with increasing rock strain, resulting in a decrease in hydraulic conductivity; then, the microcracks and fissures appear in the rock after it yields results in a sudden jump in hydraulic conductivity; in the later time, the hydraulic conductivity decreases gradually again owing to the microcracks and fissures that were compacted. The conductivity exponentially decreases with the volumetric strain during the periods of both elastic compression and postyielding. The simulated stress-strain curves using the modified model agree with the triaxial tests. The modified model was applied to the groundwater inrush of a coal mining worksite in China. The simulated water inflow agrees well with the observed data. The original model significantly underestimates the water inflow owing to it to neglect the variations of the hydraulic conductivity induced by mining.
Highlights
Coal is a reliable and affordable source of energy in many countries, such as China
The modified model was applied to the groundwater inrush of a coal mining worksite in China
In the strain-softening stage, the new fissures would begin to close under the confining pressure, and the hydraulic conductivity of the three rock samples decreased to varying degrees
Summary
Coal is a reliable and affordable source of energy in many countries, such as China. It is responsible for approximately 40 percent of the electricity generated globally. The surrounding aquifers of coal seams are the source of water inrush in the working faces. The methods to predict water inflow from working face include engineering analogy [2], empirical formulas [3, 4], hydrokinetic analysis [5, 6], analytical modeling [7,8,9], and numerical simulation [10,11,12,13].
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