Abstract
Karst collapse columns (KCCs) are naturally formed geological structures that are widely observed in North China. Given their influence on normal mining operations and the progress of mining work, collapse columns pose a hidden danger in coal mining under the influence of manual mining. By communicating often with the aquifer, the water inrush from KCCs poses a serious threat to construction projects. This paper adopts three flow field models, namely, Darcy aquifer laminar flow, Forchheimer flow, and Navier–Stokes turbulent flow, based on the changes in the water inrush flow pattern in the aquifer and laneway, and uses COMSOL Multiphysics software to produce the numerical solutions of these models. As the water inrush flow velocity increases, the Forchheimer flow shows the effect of additional force (inertial resistance) on flow in KCCs, in addition to the effect of viscous resistance. After the joint action of viscous resistance and inertial resistance, the inertial resistance ultimately dominates and gradually changes the water inrush from the KCCs to fluid seepage. Forchheimer flow can comprehensively reflect the nonlinear flow process in the broken rock mass of KCCs, demonstrate the dynamic process from the Darcy aquifer to the final tunnel turbulence layer, and quantitatively show the changes in the flow patterns of the water inrush from KCCs.
Highlights
Karst collapse columns (KCCs) are naturally formed geological structures in North China that have often developed in Ordovician limestone [1]
The Darcy laminar flow is dominated by viscous resistance, the Navier–Stokes turbulent flow is dominated by inertial resistance, and the non-Darcy Forchheimer flow is very complex and dominated by both viscous and inertial resistance [27,28]
The Darcy aquifer laminar flow field, the Forchheimer flow in the collapse column, and the Navier–Stokes turbulent flow in the laneway are adopted to examine the evolution of water inrush from the collapse column
Summary
Karst collapse columns (KCCs) are naturally formed geological structures in North China that have often developed in Ordovician limestone [1]. A part of natural low-permeability rock (coal) stratum is normally retained without excavation as the water-resisting layer to prevent water inrush from aquifer to working face. These findings highlight a close relationship between the water-resisting layer and water inrush. In the coupling operation of three flow fields, groundwater can be considered as having a Darcy laminar flow in the natural aquifer, a Forchheimer flow in the collapse column, and a laneway Navier–Stokes turbulent flow in the mining face. To qualitatively examine the influence of each factor on water inrush, this paper uses a finite element software to establish a two-dimensional (2D) plane model that reveals the changes in the fluid state, velocity, and pressure in the water inrush process by changing the permeability of the strata, the non-Darcy factor, and other parameters
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