Abstract
The stability, design, and evaluation of coal-pillar dams are affected by how water and mining affect the mechanical performance and failure mode of coal. We analyzed the composition and water-absorption mechanisms of coal samples taken from the Chahasu coal mine in western China by x-ray diffraction and nondestructive water-soaking tests. Uniaxial compression tests were carried out on coal samples with different moisture contents and loading rates to investigate their mechanical properties and deformation damage characteristics while monitoring the acoustic emissions. The compressive strength and modulus of elasticity decreased with increased moisture content, with maximum attenuations of 50.3% and 42.4%, respectively. Increasing the loading rate caused the compressive strength and elastic modulus to first increase and then decrease; the maximum increases were 74.2% and 82.5%. With low moisture content and low loading rate, the coal samples become brittle; the main failure mode was tensile failure. Increasing the moisture content enhanced the plasticity of the coal samples, leading to more shear cracks and a switch in failure mode from tensile failure to shear failure. The increased loading rate reduces the effect of water on coal samples and increases the tensile effect. High loading rates tend to produce conical failure features. Acoustic emission characteristics were used as the basis for classifying the stress stages of coal samples, which further supplements the analysis of the failure process of coal samples. Finally, the reference of this study to field engineering practice and its own limitations were analyzed. These results should help guide the design of stable underground hydraulic systems and advance our understanding of rock-fracture-failure mechanisms in a water-rich environment.
Zusammenfassung
Stabilität, Konzipierung und Bewertung von Kohlesäulendämmen werden durch die Beeinflussung der mechanischen Belastbarkeit und Schadensart der Kohle gegenüber Wasser und Bergbau bestimmt. Vorliegend wurden Zusammensetzung und Wasseraufnahme von Kohleproben aus der Chahasu Kohlemine in Westchina mittels XRD und nicht-destruktiven Wassersättigungstests analysiert. Um die mechanischen Eigenschaften und Verformungsschäden der Kohle zu untersuchen, wurden uniaxiale Druckversuche an Kohleproben mit unterschiedlichen Feuchtigkeitsgehalten und Belastungsraten bei gleichzeitiger Überwachung der Schallemissionen durchgeführt. Druckfestigkeit und Elastizitätsmodul nahmen mit steigendem Feuchtigkeitsgehalt ab, wobei die maximale Schwächung bei 50.3 bzw. 42.4% lag. Eine Erhöhung der Belastungsrate ging erst mit einer Zunahme und dann Abnahme von Druckfestigkeit (max. 74.2%) und Elastizitätsmodul (max. 82.5%) einher. Bei niedrigem Feuchtigkeitsgehalt und niedriger Belastungsrate wurden die Kohleproben spröde; die Hauptversagensart war Zugversagen. Bei erhöhtem Feuchtigkeitsgehalt nahm die Plastizität der Kohleproben zu, was zu mehr Scherrissen und einem Wechsel von Zugversagen zu Scherversagen führte. Die erhöhte Beladungsrate verringerte die Beeinflussung der Kohleproben durch Wasser und erhöhte den Zugeffekt. Hohe Belastungsraten erzeugten tendenziell konische Versagensmerkmale. Die Schallemissionen wurden als Grundlage für die Klassifizierung der Beanspruchungsstadien und damit zur Ergänzung der Analyse des Versagensprozesses der Kohleproben verwendet. Abschließend wurden die intrinsischen Limitierungen und der Bezug dieser Studie auf die Ingenieurspraxis im Gelände analysiert. Die Ergebnisse sollen dazu beitragen, die Planung stabiler (unterirdischer) hydraulischer Systeme und unser Verständnis der Bruchmechanismen in einer wasserreichen Umgebung zu verbessern
Resumen
La estabilidad, el diseño y la evaluación de diques de pilares de carbón se ven afectados por el modo en que el agua y la minería influyen en el rendimiento mecánico y el modo de fallo en el caso del carbón. Analizamos la composición y los mecanismos de absorción de agua de muestras de carbón extraídas de la mina de carbón de Chahasu, en el oeste de China, mediante difracción de rayos X y pruebas no destructivas de remojo en agua. Se realizaron ensayos de compresión uniaxial en muestras de carbón con diferentes contenidos de humedad y tasas de carga para investigar sus propiedades mecánicas y las características de los daños por deformación mientras se monitorizaban las emisiones acústicas. La resistencia a la compresión y el módulo de elasticidad disminuyeron al aumentar el contenido de humedad, con atenuaciones máximas del 50.3% y el 42.4%, respectivamente. El aumento de la tasa de carga hizo que la resistencia a la compresión y el módulo de elasticidad aumentaran primero y disminuyeran después; los aumentos máximos fueron del 74.2% y el 82.5%. Con un bajo contenido de humedad y una baja tasa de carga, las muestras de carbón se volvieron quebradizas siendo la rotura por tracción el principal modo de fallo. El aumento del contenido de humedad incrementó la plasticidad de las muestras de carbón, lo que provocó más grietas de cizallamiento y un cambio en el modo de fallo cambiando de tracción a cizallamiento. El aumento de la tasa de carga reduce el efecto del agua en las muestras de carbón y aumenta el efecto de tracción. Las altas tasas de carga tienden a producir características de fallo cónico. Las características de emisión acústica se utilizaron como base para clasificar las etapas de tensión de las muestras de carbón, lo que complementa aún más el análisis del proceso de fallo de las muestras de carbón. Por último, se analizó la transferencia de este estudio a la práctica de la ingeniería de campo y sus propias limitaciones. Estos resultados deberían ayudar a orientar el diseño de sistemas hidráulicos subterráneos estables y a avanzar en nuestra comprensión de los mecanismos de fractura-fractura de la roca en un entorno rico en agua.
摘要
水和采动对煤体力学特性和破坏模式的作用, 影响着煤柱体的稳定性、设计和评价。通过X射线衍射和无损浸水试验分析了中国西部察哈素煤矿煤样的组成和吸水机理。对不同含水率和加载速率的煤样进行单轴压缩试验, 在监测声发射的同时考察其力学特性和变形破坏特征。抗压强度和弹性模量随含水率的增加而减小, 最大衰减量分别为50.3%和42.4%。增大加载速率导致抗压强度和弹性模量先增大后减小; 最大增幅分别为74.2%和82.5%。在低含水率和低加载速率下, 煤样变脆; 主要破坏模式为拉伸破坏。含水率的增加增强了煤样的塑性, 导致更多的剪切裂纹产生, 破坏模式由拉伸破坏转变为剪切破坏。加载速率的增加降低了水对煤样的作用, 增加了拉伸作用。高加载速率易产生锥形破坏特征。将声发射特征作为划分煤样受力阶段的依据, 进一步补充了煤样破坏过程的分析。最后分析了本研究对现场工程实践的借鉴意义和自身的局限性。研究结果将有助于指导设计稳定的地下液压系统, 并促进我们对含水环境中岩石断裂破坏机制的理解。
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This research was funded by the National Natural Science Foundation of China (grant 51674248). The authors gratefully thank the reviewers for their constructive comments.
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Yao, Q., Yu, L., Shan, C. et al. Experimental Study on the Mechanical Damage and Deformation Failure of Water-bearing Coal Samples. Mine Water Environ 42, 251–265 (2023). https://doi.org/10.1007/s10230-023-00933-7
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DOI: https://doi.org/10.1007/s10230-023-00933-7