Abstract
Underground water reservoir (UWR) technology has been used to protect mine water resources. The main underground space for UWRs is the caving zone formed by longwall mining. Broken rock mass movement in the caving zone affects the porosity distribution and seepage characteristics during the UWR’s circulation, storage, and discharge. We used a fluid-solid coupled model, implemented in PFC3D and combined with Python, to simulate water seepage in the caving zone. The influence of particle size and fluid element size on the error of the simulation results was analysed. Then, we investigated the effect of seepage on broken rock mass porosity under different stress states. Simulations with various particle sizes and compaction stresses show that the average displacement of broken rock decreases exponentially with increased stress. Because large broken particles form the primary bearing structure in the model, it is mostly small particles that move under high-stress levels, so porosity is less affected. Larger particles also migrate if the compaction stress is low; this significantly changes the porosity and leads to roof uplift. Finally, we designed an engineering scale model based on our simulation method using the actual UWR situation in a coal mine.
Zusammenfassung
Die Technologie der untertägigen Wasserreservoirs (UWR) wird zum Schutz der Wasserressourcen im Bergbau eingesetzt. Der wichtigste untertägige Raum für UWRs ist die Bruchzone, die durch den Strebbau entsteht. Die Bewegung im Alten Mann beeinflusst die Porositätsverteilung und die Sickereigenschaften während der Wasserzirkulation, der Speicherung und der Entleerung des UWR. Zur Simulation des Fließverhaltens im Alten Mann wurde ein gekoppeltes Flüssigkeits-Feststoff-Modell verwendet, das in PFC3D implementiert und mit Python kombiniert wurde. Der Einfluss der Partikelgröße und der Fluid-Elementgröße auf den Fehler der Simulationsergebnisse wurden analysiert. Anschließend wurde die Auswirkung des Sickerwassers auf die Durchlässigkeit des Alten Mannes unter verschiedenen Spannungszuständen untersucht. Simulationen mit verschiedenen Korngrößen und Spannungszuständen zeigen, dass die durchschnittliche Massenverlagerung im Alten Mann mit zunehmender Spannung exponentiell abnimmt. Da im Modell große Bruchstücke die primäre Tragstruktur bilden, bewegen sich bei hohen Spannungen hauptsächlich kleine Partikel, so dass die Porosität weniger beeinflusst wird. Größere Partikel wandern bei niedrigen Druckspannungen; dies verändert die Porosität erheblich und führt zu einer Hebung der Firste. Schließlich wurde auf Grundlage der eingesetzten Simulationsmethode und der tatsächlichen UWR-Verhältnisse in einer Kohlengrube ein maßstäbliches Modell entwickelt.
Resumen
La tecnología de los depósitos de agua subterráneos (UWR) se ha utilizado para proteger los recursos hídricos de las minas. El principal espacio subterráneo para los UWR es la zona cavada formada por la minería de tajo largo. El movimiento de la masa de roca rota en la zona de espeleología afecta a la distribución de la porosidad y a las características de la filtración durante la circulación, el almacenamiento y la descarga del UWR. Utilizamos un modelo acoplado fluido-sólido, implementado en PFC3D y combinado con Python, para simular la filtración de agua en la zona cavada. Se analizó la influencia del tamaño de las partículas y del tamaño de los elementos del fluido en el error de los resultados de la simulación. A continuación, se investigó el efecto de la infiltración en la porosidad de la masa rocosa rota bajo diferentes estados de tensión. Las simulaciones con diversos tamaños de partículas y tensiones de compactación muestran que el desplazamiento medio de la roca rota disminuye exponencialmente con el aumento de la tensión. Dado que las partículas rotas de gran tamaño forman la principal estructura portante en el modelo, son sobre todo las partículas pequeñas las que se desplazan bajo niveles de tensión elevados, por lo que la porosidad se ve menos afectada. Las partículas más grandes también migran si el esfuerzo de compactación es bajo; esto cambia significativamente la porosidad y conduce al levantamiento del techo. Por último, diseñamos un modelo a escala de ingeniería basado en nuestro método de simulación utilizando la situación real de UWR en una mina de carbón.
摘要
地下水库(UWR)技术已被用于保护矿井水资源。地下水库的主要地下空间是长壁开采形成的冒落区。冒落区的破碎岩体运动影响地下水库水循环、储存和排泄过程的孔隙度分布和渗流特性。使用PFC3D及结合Python方法建立了流固耦合模型, 模拟冒落区渗水。分析了颗粒尺寸和流元大小对模拟误差的影响。研究了不同应力状态下渗流对破碎岩体孔隙度的影响。不同的颗粒大小和压实应力的模拟结果表明, 破碎岩石的平均位移随着应力增加而指数减小。由于大破碎颗粒形成了模型的主要承载结构, 高应力作用下移动的主要是小颗粒, 使孔隙率受影响较小。如果压实应力较低, 大颗粒也发生了位移, 将明显改变孔隙率, 导致顶板隆起。最后, 利用模拟方法, 建立了一个煤矿实际地下水库的工程规模模型。
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Acknowledgements
Financial support for this study was provided by the Beijing Municipal Natural Science Foundation (8212032), the National Natural Science Foundation of China (U1910206, 52104155, 51874312), the Open Fund of State Key Laboratory of Water Resources Protection and Utilization in Coal Mining (WPUKFJJ2019-15), and the Fundamental Research Funds for the Central Universities (2021YQNY11). We also thank the anonymous reviewers for their constructive comments and suggestions on the draft manuscript.
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Zhang, C., Jia, S., Bai, Q. et al. CFD-DEM Coupled Simulation of Broken Rock Mass Movement During Water Seepage in an Underground Goaf Reservoir. Mine Water Environ 40, 1048–1060 (2021). https://doi.org/10.1007/s10230-021-00826-7
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DOI: https://doi.org/10.1007/s10230-021-00826-7