Abstract
In the Jiaozuo mining area of the North China coal field, there are multiple water-rich aquifers close to the coal seam. To prevent water inrush accidents, the subfloor strata needs to be reinforced by grouting before mining. According to how the mechanics and hydrogeological properties of the key floor rock strata changed after grouting, the coal seam floor was divided into two zones: a ‘water conductive fracture zone’ and a ‘mechanically strong damaged zone’. A composite model of a key structurally stable water-control floor layer and a key infiltration-water damage-control floor layer was established after grouting of the uppermost (L8) subfloor aquifer. Microseismic (MS) technology was used to analyze the characteristics of the two zones and the water control capability of the two key layers in faulted and non-faulted regions of the experimental working face, which revealed that the grouted L8 limestone served as a key mechanical barrier layer. The change in the elastic modulus of the rock mass before and after grouting was measured by the borehole ultrasonic method, which showed that the elastic modulus of the rock mass increased by 40–852% after grouting. Based on FLAC3D numerical simulation and field measurements, grouting reduced the failure depth of the floor by 51%. Seven factors that influence the floor water control ‘dual key layers’ were proposed, which were quantified using the analytic hierarchy process (AHP) method. We found that fault activation and water-filled faults were the main factors affecting the water control capability of the dual key layer. The results of the research will contribute to the early warning, prevention, and evaluation of floor water inrushes in mines with similar hydrogeological conditions.
Zusammenfassung
Im Jiaozuo-Bergbaugebiet im nordchinesischen Kohlerevier gibt es mehrere wasserreiche Grundwasserleiter in der Nähe des Kohleflözes. Um Unfälle durch Wassereinbrüche zu verhindern, müssen die Liegendschichten vor dem Abbau durch Verpressen verstärkt werden. Je nachdem, wie sich die mechanischen und hydrogeologischen Eigenschaften der liegenden Gesteinsschichten nach der Verpressung ändern, wird die Flözbasis in zwei Zonen unterteilt: eine "wasserleitende Bruchzone" und eine "mechanisch stark beschädigte Zone". Nach der Verpressung des obersten (L8) Grundwasserleiters wird ein zusammengesetztes Modell unter Verwendung einer strukturell stabilen wasserführenden und einer infiltrations- und schadensbegrenzenden Basisschicht erstellt. Mit Hilfe von Mikroseismik (MS) können die Eigenschaften und die Wasserkontrollfähigkeit der beiden Schlüsselzonen in gestörten und ungestörten Bereichen der Ortsbrust experimentell analysiert werden. Dabei zeigt sich, dass der durch die Verpressung behandelte Kalkstein L8 als wichtige mechanische Sperrschicht dient. Die Veränderung des Elastizitätsmoduls des Kalksteins vor und nach der Verpressung wird durch Bohrloch-Ultraschall untersucht. Es zeigt sich, dass das Elastizitätsmodul nach der Verpressung um 40 % bis 852 % anstieg. Numerische FLAC3D-Simulation und Feldmessungen deuten darauf hin, dass somit die Versagenstiefe des Untergrundes um 51 % reduziert werden kann. Es können sieben Faktoren, welche die Wasserführung in der Basisschicht beeinflussen, identifiziert und mit Hilfe einer AHP-Methode (Analytic Hierarchy Process) quantifiziert werden. Hauptfaktoren, die die Wasserkontrollfähigkeit der beiden Schlüsselschichten beeinflussten, sind die Reaktivierung von Störungszonen und die Wasserführung in Störungsbereichen. Die Forschungsergebnisse können zur Frühwarnung, Prävention und Bewertung von Liegendwassereinbrüchen in Bergwerken mit ähnlichen hydrogeologischen Randbedingungen beitragen.
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Data Availability
The data used to support the findings of this study are available from the corresponding author upon request.
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Acknowledgements
The authors are grateful to the Jiulishan coal mine for their partial funding, providing field testing sites, and related data. This work was supported by the National Natural Science Foundation of China (Fund 51934008).
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Miao, W., Xu, Y., Guo, D. et al. The Two Zones of Floor Failure and its Control via a ‘Dual Key Layer’ Approach. Mine Water Environ 43, 117–135 (2024). https://doi.org/10.1007/s10230-024-00974-6
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DOI: https://doi.org/10.1007/s10230-024-00974-6