Storage coefficient modeling and capacity evaluation of coal mine underground reservoirs considering gangue deformation and goaf structure

Abstract

Coal mine underground reservoirs help address the severe water imbalance in ecologically fragile mining regions of western China, but evaluating their storage capacity remains challenging due to the coupled effects of gangue deformation, saturation, and goaf geometry. This study investigates the deformation and void evolution of fragmented gangue with varying lithologies, particle sizes, and water contents through an independent-developed testing system and theoretical model. A planar micro-unit model and a three-dimensional spatial structure model are proposed to quantify the storage coefficient and total reservoir capacity of underground water storage structures. These models incorporate the effects of stratified lithologies, saturation-induced softening, and spatially distributed stress conditions. The methodology is applied to the underground reservoir in Chahasu coal mine, and the results show that under increasing stress, storage coefficients decline exponentially, with pronounced differences between single- and double-lithology structures. The storage coefficient in the spatial model demonstrate greater resilience to stress concentration compared to planar models, and further analysis identifies critical thresholds in roof fracture distances and stress-recovery times affecting long-term storage performance. This research provides a comprehensive framework for evaluating underground reservoir storage potential, offering theoretical support and engineering guidance for the sustainable utilization of mine water.

Keywords

Coal mine underground reservoir / Storage coefficient / Fragmented gangue / Caving zone / Water-rock interaction

CRediT authorship contribution statement

Yinghu Li: Writing – original draft, Software, Methodology, Formal analysis. Qiangling Yao: Supervision, Resources, Funding acquisition. Feng Zong: Formal analysis, Resources. Ze Xia: Writing – original draft, Resources, Investigation, Funding acquisition. Qiang Xu: Visualization, Funding acquisition. Liqiang Yu: Writing – review & editing, Funding acquisition. Kaixuan Liu: Formal analysis. Haitao Li: Data curation.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (Nos. 52404153, 52504157 and 52504156) and the Natural Science Foundation of Jiangsu Province (No. BK20241649).

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