Abstract
Quaternary unconsolidated porous aquifers are crucial to industrial, agricultural, and domestic water as well as ecological requirements in semiarid regions. Underground mining can influence aquifers even when they are located out of the fractured zone. Slight but continuous leakage should not be ignored. This study focused on the flow from a leaky aquifer. The deformation and fissure distribution characteristics and changes in the water resistance of a clay aquitard underlying an unconsolidated aquifer were studied by physical modeling, and the impacts on the unconsolidated aquifer were analyzed. Considering the mining-induced changes in the overburden hydraulic conductivity, we used numerical groundwater flow simulations of an unconsolidated aquifer to predict the flow dynamics of the aquifer for different scenarios. The influences of aquitard thickness and permeability on the groundwater flow regime of the regional unconsolidated aquifer under the mining area were quantitatively analyzed. This case study shows that the degree of coal extraction influence on the leaky confined aquifer depends on the properties of the aquitard beneath the aquifer. When the thickness was as high as 40 m and the hydraulic conductivity was as low as 10−6 cm/s, the aquitard could effectively prevent a water level depression. The results have practical implications for coal mining with water resource conservation.
抽象
第四系松散孔隙含水层对于半干旱区的工业用水、农业用水、生活用水以及生态需求至关重要。井工煤炭开采对导水裂隙带之上的含水层也会产生影响。轻微但持续的渗漏不可忽视。集中研究了越流含水层越流量。利用物理模拟,研究了松散含水层下粘性弱透水层的变形、裂隙分布和阻水能力变化,评价了它们对上覆松散含水层的影响。考虑采动引起的覆岩渗透系数的变化,采用数值模拟方法模拟松散含水层,预测不同情形下的水动力场特征。定量分析了开采条件下弱透水层厚度和渗透性对区域松散孔隙含水层地下水的影响。研究实例表明,采煤对越流含水层的影响程度取决于含水层下伏弱透水层的性质。当厚度达40 m,渗透系数低至10-6 cm/s时,弱透水层能有效地防止上覆含水层水位下降。研究结果对保水采煤具有实践指导意义。
Zusammenfassung
Quartäre unkonsolidierte Porenaquifere sind in semi-ariden Regionen für Industrie, Landwirtschaft, häusliche Wasserversorgung und ökologische Bedürfnisse äußerst wichtig. Untertagebergbau kann Aquifere auch dann beeinflussen, wenn diese über dem geklüftetem Fels liegen. Eine geringe aber stetige Sickerung darf nicht außer Acht bleiben. Diese Studie betrifft Abfluß aus einem lecken Aquifer. Deformation, Kluftverteilung und Veränderungen der Wasserresistenz eines tonigen Aquitards, welcher einen unkonsolidierten Aquifer unterlagert, wurden durch physikalische Modellierung untersucht. Die Auswirkungen auf den unkonsolidierten Aquifer wurden analysiert. Hinsichtlich bergbau-induzierter Veränderungen der hydraulischen Konduktivität des Deckgebirges benützten wir numerische Grundwasserflußsimulationen eines unkonsolidierten Aquifers um für verschiedene Szenarios die Fließdynamik des Aquifers vorher zu sagen. Quantitativ analysierten wir den Einfluß von Mächtigkeit und Durchlässigkeit des Aquitards auf das Grundwasserfließregime im Bergbaugebiet. Die Fallstudie zeigt, daß der Einflußgrad des Kohlenabbaues auf den leckenden gespannten Aquifer von den Eigenschaften des Aquitards unter dem Aquifer abhängt. Der Aquitard verhindert eine Absenkung des Wasserspiegels, wenn die Mächtigkeit 40 m und die hydraulische Konduktivität 10-6 cm/s beträgt. Es resultieren praktische Folgerungen für Kohlenbergbau mit Schutz von Wasserressourcen.
Resumen
Los acuíferos porosos no consolidados cuaternarios son cruciales para el agua industrial, agrícola y doméstica, así como para los requisitos ecológicos en las regiones semiáridas. La minería subterránea puede influir en los acuíferos incluso cuando se encuentran fuera de la zona fracturada. Las fugas leves pero continuas no deben ignorarse. Este estudio se centró en el flujo de un acuífero con fugas. Las características de deformación y distribución de fisuras y los cambios en la resistencia al agua de un acuitardo de arcilla subyacente a un acuífero no consolidado se estudiaron mediante modelado físico; se analizaron los impactos en el acuífero no consolidado. Teniendo en cuenta los cambios inducidos por la minería en la conductividad hidráulica de sobrecarga, utilizamos simulaciones numéricas de flujo de agua subterránea de un acuífero no consolidado para predecir la dinámica de flujo del acuífero para diferentes escenarios. Se analizaron cuantitativamente las influencias del espesor y la permeabilidad del acuitardo en el régimen de flujo de agua subterránea del acuífero regional no consolidado bajo el área minera. Este estudio de caso muestra que el grado de influencia de la extracción de carbón en el acuífero confinado con fugas depende de las propiedades del acuitardo debajo del acuífero. Cuando el grosor fue tan alto como 40 m y la conductividad hidráulica tan baja como 10-6 cm/s, el acuitardo podía prevenir efectivamente una depresión del nivel del agua. Los resultados tienen implicaciones prácticas para la minería del carbón con conservación de los recursos hídricos.
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Acknowledgements
This research was funded by the National Natural Science Foundation of China, Grant 41572221; Research Fund of Key Research Program of Ministry of Science and Technology for Water Resources Efficient Development and Utilization Project [2018YFC0406403]; and the National Natural Youth Science Foundation of China, grant 41502243. We gratefully acknowledge the financial support and thank Engineers Haodong Sun and Xue Wang and Assistant researcher Jun Zhu for aiding in conducting this research. We also thank the editors and peer reviewers for their time, careful work, and helpful suggestions.
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Supplementary material 2 Supplemental Figure S-2 Groundwater level fitting curves (a) Calibration period (b) Validation period (c) The fitting of the water level duration curves for typical observation wells (PDF 110 kb)
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Xu, S., Zhang, Y., Shi, H. et al. Impacts of Aquitard Properties on an Overlying Unconsolidated Aquifer in a Mining Area of the Loess Plateau: Case Study of the Changcun Colliery, Shanxi. Mine Water Environ 39, 121–134 (2020). https://doi.org/10.1007/s10230-019-00649-7
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DOI: https://doi.org/10.1007/s10230-019-00649-7