Abstract
The coordinate mining of stack resources in the Ordos Basin, which involves the coupling effects of stress fracture, seepage, and reactive solute transport, plays an important role in resource exploration and environment protection. A coupled multiphysical–chemical model, involving a modified non-Darcy flow model, a leaching solution reaction, and a reactive solute transport model, was developed in this study. The Fast Lagrangian Analysis of Continua -Computational Fluid Dynamics (FLAC3D-CFD) simulator coupled with the developed models was used to investigate the evolution and morphology of mining-induced multifield coupling for the scenarios of concurrent mining and asynchronous mining of coal and uranium. As mining advanced to 160 m, the maximum principle stress characterized by a stress shell was observed. As mining progressed to 280 m, a rupture occurred, and a new stress shell was generated as a rear skewback was formed by the concentrated stress of the stope. An “arch-shaped” fracture field combined with a “saddle-shaped” seepage field was identified in the destressed zone of the stress shell. In the coordinated mining of uranium prior to coal, “funnel-shaped” and “asymmetric saddle-shaped” morphologies of the leaching solution were found during coal mining for ventilation in the stope and mining face. By contrast, “saddle-shaped”, “inclined funnel-shaped”, and “horizontal” morphologies of the leaching solution were observed for a short period for ventilation of the stope and mining face for coal mining prior to uranium mining, uranium mining prior to coal mining, and synchronized coal and uranium mining. A dynamic stress response was obtained in the coal seam, followed by the conglomerate aquifer and the uranium deposits. The diffusion depth of the solution was negatively correlated with the injection velocity and the pumping ratio and positively correlated with the diffusion coefficient. A dynamic increase in diffusion depth was observed as the diffusion coefficient increased to 1 × 10−4 m2/s.
Highlights
With advanced mining equipment and technologies, longwall mining of coal seams [1,2,3,4] and in situ leaching of uranium [5,6,7] have been widely accepted
Based on the stack occurrence of coal and uranium in the Ordos Basin, this study investigated the evolution and morphology of the stress–fracture–seepage solute reaction transport field under different coordinated mining scenarios using a developed multiphysical–chemical model coupled with the FLAC3D-CFD simulator
Coal mining induced changes in the stress, seepage, and fracture fields, the mined uranium was dissolved in the solute, and the mixture was transported into the seepage field
Summary
With advanced mining equipment and technologies, longwall mining of coal seams [1,2,3,4] and in situ leaching of uranium [5,6,7] have been widely accepted. Kim et al [21] proposed a finite, elastic, and porous model to study coupled rock deformation and groundwater flow from mining in saturated and fractured geological media. The characteristics of the physical and chemical responses of mined deposits under different pumping ratios, pressure differences, and well spaces were extensively studied using an integrated method of experimentation and numerical simulation [28,29,30]. The hydrogeological response to the coordinate mining of coal and uranium, which utilizes the coupling effect of the stress–fracture–seepage field, solute chemical reaction, and transport and is crucial to safety and environment protection in mining, is rarely studied. Based on the stack occurrence of coal and uranium in the Ordos Basin, this study investigated the evolution and morphology of the stress–fracture–seepage solute reaction transport field under different coordinated mining scenarios using a developed multiphysical–chemical model coupled with the FLAC3D-CFD simulator. The dependence of changes in stratum stress and uranium-bearing solution on the mining technology was analyzed
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