Jiuchuan Wei

Comprehensive evaluation of water-inrush risk from coal floors

Abstract Lower groups of coal seams are presently being mined in the Yanzhou coal mining area. We need to evaluate the risk from water-inrush from coal floors in order to have safe production in the lower groups of coal seams in mines. Based on a systematic collection of hydrogeological data and some data from mined working faces in these lower groups, we evaluated the factors affecting water-inrush from coal floors of the area by a method of dimensionless analysis. We obtained the order of the factors affecting water-inrush from coal floors and recalculated data on depths of destroyed floors by multiple linear regression analysis and obtained new empirical formulas. We also analyzed the water-inrush coefficient of mined working faces of the lower groups of coal seams and improved the evaluation standard of the water-inrush coefficient method. Finally, we made a comprehensive evaluation of water-inrush risks from coal floors by using the water-inrush coefficient method and a fuzzy clustering method. The evaluation results provide a solid foundation for preventing and controlling the damage caused by water of an Ordovician limestone aquifer in the lower group of coal seams in the mines of Yanzhou. It provides also important guidelines for lower groups of coal seams in other coal mines.

Formation and Height of the Interconnected Fractures Zone after Extraction of Thick Coal Seams with Weak Overburden in Western China

Formation of a zone of interconnected fractures during coal mining is a key factor in mine flooding. Coal mines in western China are characterized by thick coal seams with mechanically weak overburden. In situ studies including drill core analysis, drilling fluid loss measurement, and borehole video monitoring were used at the working face 101 in Shaanxi Jinjitan coal mine to explore the maximum height of the interconnected fractures zone (IFZ). Also, tests on a scaled physical model and numerical simulation based on the drilling data were used to study the formation of the fractured zone. By considering data from other mines with similar mining conditions, a logarithmic relationship was found between the maximum height of the IFZ and the thickness of coal excavation. The maximum height of the IFZ was found to be 27 times the thickness of the excavated coal seam, which is far more than in coal mining areas in eastern China. Also, the IFZ in overlying strata of the study area was arch-shaped, not saddle-shaped, as had been observed in previous studies.ZusammenfassungDie Ausbildung einer Zone von verbundenen Bruchzone während des Kohleabbaus ist ein Schlüsselfaktor bei der Grubenflutung. Die Kohlebergwerke in Westchina sind durch mächtige Kohleflöze und bruchanfälligem Deckgebirge charakterisiert. Diese unterscheiden sich deutlich von Kohlebergwerken in Ostchina. Vor-Ort-Untersuchungen, welche Bohrkernanalysen, Messung von Bohrspülungsverlusten und Kameraüberwachungen im Bohrloch beinhalteten, wurden am Arbeitsgebiet 101 im Shaanxi Jinjitan-Kohlebergwerk genutzt, um die maximale Ausdehnung der Bruchzone zu erkunden. Weiterhin wurden Tests an einem maßstabsgetreuen physikalischen Modell und numerische Modellrechnungen basierend auf den Bohrdaten durchgeführt, um die Bildung der Bruchzone zu untersuchen. Unter Berücksichtigung von Daten aus anderen Bergwerken mit ähnlichen Abbaubedingungen wurde eine logarithmische Beziehung zwischen der maximalen Ausdehnung der Bruchzone und der Mächtigkeit des Kohleabbaus gefunden. Die maximale Ausdehnung der Bruchzone beträgt demnach etwa das 27-fache der Mächtigkeit des abgebauten Kohleflözes, die damit deutlich größer ist als in den Kohlebergbaugebieten in Ostchina. Darüber hinaus war im Gegensatz zu früheren Studien die Bruchzone im Hangenden des Untersuchungsgebietes bogenförmig und nicht sattelförmig.ResumenLa formación de una zona de fracturas interconectadas durante la explotación minera de carbón, es un factor clave en la inundación de la mina. Las minas de carbón en el este de China están caracterizadas por la presencia de gruesas vetas de carbón en rocas mecánicamente débiles, que difiere mucho de las minas de carbón en el este de China. Estudios in situ que incluyeron el análisis del corazón de la perforación, la medida de la pérdida de fluido en la perforación y el videomonitoreo del pozo, se usaron en la cara de trabajo 101 en la mina de carbón Shaanxi Jinjitan, para conocer la máxima altura de la zona de fracturas interconectadas (IFZ). Los ensayos sobre un modelo físico escalado y la simulación numérica sobre los datos de la perforación también fueron usados para estudiar la formación de la zona de fractura. Teniendo en cuenta datos de otras minas con iguales condiciones, se encontró una relación logarítmica entre la altura máxima del IFZ y el grosor de la excavación. La máxima altura del IFZ fue 27 veces mayor que el grosor de la veta de carbón excavada que es mucho mayor que la que se encuentra en áreas mineras del este de China. También, el IFZ en estratos superpuestos del área de estudio fue en forma de arco y no en forma de montura como fuera observado en estudios previos.摘要煤矿突水的一个重要因素是与矿井开采过程中形成的导水裂缝带(IFZ)有关。而在中国西部矿区具有煤厚、覆岩强度低等特点,与东部矿区有显著不同。为了探测位于中国西部的陕西金鸡滩煤矿开采101工作面形成的最大导水裂缝带高度,采用钻孔岩芯分析、钻孔冲洗液漏失量观测和钻孔彩色电视三种手段对其现场实测。同时,依据钻井数据建立物理模型和数值模型研究裂缝带的形成机理。结合周边其他相似矿区的裂缝带实测数据,发现西部矿区导水裂缝带高度与煤层开采厚度之间存在一个对数的关系,并且裂缝带最大高度可以达到27倍以上的采厚,其数值远高于东部矿区。另外,在所研究区域得到的裂缝带的发育形态为弧形,并非先前认为的马鞍形

Numerical Simulation of Water Flow from the Coal Seam Floor in a Deep Longwall Mine in China

The study of groundwater flow from the coal seam floor is critical to safe mining operations in China. We developed a numerical simulation model to describe flood water pathways during mining, using the field conditions present at the no. 4196 west work face in the Panxi longwall coal mine, Shandong Province, China, Groundwater flow analysis revealed unusual values for the failure depth of the coal seam floor. The high ground stress and underground pressure, excavation length, width of working face, poor mechanical properties of aquitards, and expansion of fractures by groundwater infiltration all contribute to groundwater flow into the mine. The modeling results predict the time and longwall locations associated with the maximum likelihood of flood occurrence. Such results can be used by decision makers to improve mine design and safety.ZusammenfassungEntwickelt wurde ein numerisches Simulationsmodell zur Beschreibung von während des Abbaubetriebs auftretenden Wasserzuflüssen, und zwar unter Verwendung der realen Bedingungen im Streb Nr. 4196 West der Kohlengrube Panxi, Provinz Shandong, China. Die Analyse der Grundwasserströmung offenbarte ungewöhnliche Werte für die Versagensteufe des Flözliegenden. Hohe Bodenpressung, die Erstreckung des Abbauraums in Verhiebsrichtung, die Breite der Abbaufront, eine geringe mechanische Standfestigkeit der Grundwasserhemmer sowie Kluftöffnung infolge Grundwasserinfiltration tragen zum Grundwasserzufluss zur Grube bei. Als Modellergebnis werden Zeitpunkt und Streb-Lokation von Zuflussereignissen maximaler Wahrscheinlichkeit prognostiziert. Derartige Ergebnisse können von den zuständigen Entscheidungsträgern zur Verbesserung der Bergwerksplanung und zur Erhöhung der Arbeitssicherheit genutzt werden.ResumenHemos desarrollado un modelo de simulación numérica para describir las etapas de la inundación durante la explotación minera, usando las condiciones de campo presentes en la cara de trabajo oeste n° 4196 en la mina de carbón de frente largo Panxi, provincia de Shandong, China. El análisis del flujo de agua subterránea reveló inusuales valores para la profundidad de la falla en el piso de la veta de carbón. El elevado estrés del piso, la presión subterránea, la longitud de la excavación, el ancho de la cara de trabajo, las pobres propiedades mecánicas de los acuitardos y la expansión de fracturas por la infiltración de agua subterránea, contribuyen al flujo de agua subterránea dentro de la mina. Los resultados del modelado predicen el tiempo y los lugares de frente alto asociados con la máxima probabilidad de ocurrencia de inundaciones. Estos resultados pueden ser usados para que los tomadores de decisiones mejoren el diseño de la mina y de la seguridad.摘要建立了潘西矿(中国山东)4196西长壁工作面底板突水数值模型,模拟开采期间突水路径的形成及演化过程 。地下水流分析可以揭示煤层底板破坏深度。高地应力与高矿山压力、工作面开采长度、工作面宽度、底板弱透水层力学性能及地下水入渗透引起的原始裂隙扩展等都是影响煤矿突水的重要因素。模拟结果预测了深矿井开采最有可能发生突水时间和突水位置。研究成果有利于决策者改进生产设计和提高生产安全性。

In situ dynamic monitoring of stress revolution with time and space under coal seam floor during longwall mining

AbstractIn situ dynamic monitoring was used to obtain spatial and temporal strain and stress data in the floor strata during longwall mining at the no. 1604 working face in Nantun Coal Mine, China. The results reveal the presence of four stress stages distributed at four sections along the mining direction: weak response stage, significant increase stage, dramatic decrease stage, and slow restoration stage. Three vertical structural zones are identified under the excavation floor: (1) fracture zone, (2) deformation zone, and (3) lightly affected zone. Based on detailed analysis of the collected data, the relationship between the maximum vertical stress increment and depth is inversely exponential, whereas the relationship between the maximum horizontal stress increment and depth is linear. The monitoring results are conducive to determining the maximum depth of fracture zone under the coal seam floor and width of the significant stress increase stage, which are important factors in controlling groundwater inrush in operating coal mines.

Evaluation of Water Inrush Risk from Coal Floor and Prediction Software Development

Based on systematic collection of the hydrogeological data of coal mine, we analyzed the factors affecting water inrush from coal floor and determined the major factors. We used the fuzzy clustering method to evaluate the water inrush risk from coal floor in order to solve the evaluating limitation of water inrush risk from coal floor by the water inrush coefficient method. The fuzzy clustering method gave a comprehensive consideration of many factors affecting water inrush from coal floor and it solved the problems of evaluating critical values by the water inrush coefficient method. To rapidly predict the water inrush risk from coal floor and improve the prediction accuracy, we developed the prediction software for water inrush risk from coal floor. On the theoretical basis of water inrush coefficient method and fuzzy clustering method, we used Visual Basic 6.0 design language as development platform, combining Access database and Matlab software, to develop prediction software, which had a zoning evaluation of water inrush risk. Take the Xinglongzhuang coal mine for example, the major factors affecting water inrush risk from coal floor were head pressure of Ordovician limestone aquifer, aquifuge thickness, geological structure and water abundance of Ordovician limestone aquifer. And we had a zoning evaluation of its water inrush risk. The evaluation results provide scientific basis for working out measures to prevent and control the water of Ordovician limestone aquifer to Xinglongzhuang coal mine. It also has important guiding significance to exploitation safety of coal mining. Because the prediction software has common applicability, it provides powerful support for rapidly correct evaluation of water inrush risk to other coal mines.

Application of GIS in Prediction of Ordovician Limestone Water Inrush from Seam Floor in Nanding Coal Mine(China)

For exploiting safely in deep area of Nanding coal mine in Shangdong province of China, this paper have used multi-originated information complex to predict fatalness of water inrushing from seam floor during mining. This paper analyzed main factors which affect water inrush from seam floor with the function of multi-originated of GIS in Surfer software to modify the method of water inrush coefficient and built model of water inrush index adapt to the coal mine. The coal mine was divided into three areas, dangerous areas and relative dangerous areas and safe areas with the model when the tenth coal seam was mined. The results show that water inrush from floor are result by various factors working together, geologic structure play a control action, hydraulic pressure and mining pressure are the dynamic condition, aquifuge takes the restriction effect. The result of prediction will guide Nanding coal mine exploit safely in deep area.

The Application of Dimensionless Analysis to Evaluation of Factors Affecting Water-Inrush from Coal Floor

Dimensionless analysis was applied to correctly evaluate the order of the factors affecting water -inrush from coal floor. In the evaluation of water -inrush from coal floor, many factors need to be considered. Thus, to correctly evaluate the order of the factors affecting water -inrush from coal floor is very important, which is the key to reasonable evaluation of water -inrush from coal floor. Based on systematic collection of the hydrogeological data of Yanzhou Coal Mining Area, we analyzed the factors affecting water -inrush from coal floor and evaluated water-inrush risk of lower group of coal seams mining. We used dimensionless analysis for the standardized process of hydrogeological data. There also came a comparison of each factor affecting water -inrush from coal floor under information fusion. Then we obtained the order of factors affecting water-inrush from coal floor. The results shows that dimensionless analysis is good for evaluating many factors affecting water -inrush from coal floor. It provides the powerful foundation for evaluation of water -inrush risk from coal floor in lower group of coal seams mining.

Application of Strip-Partial Mining to Prevent Water Inrush from Coalbed Floor in Nanding Coal Mine

For exploiting safely in deep area where the coalbed were threatened by confined aquifer under coalbed floor of Nanding coal mine in Shandong province of China, this paper has put forward the strip-partial mining method and have calculated the mining width and coal pillar width based on the allowable distortion of the earths surface and prevent water inrush from coalbed floor. First, this paper put forward the strippartial mining method because the mining width of workface was the main factor affect permeable failure depth in the coalbed floor. Second, according to the formula of permeable failure depth in the coalbed floor and safe aquifuge thickness with formula in Rule, the paper calculated the mining width in different depth based on the thickness of aquifuge, safe aquifuge thickness, permeable failure depth in the coalbed floor, the allowable distortion of the earths surface and damage of rockmass. Last, the coal pillar width was calculated by the actual load and limit load where the safe factor was 1.2 under the conditions of different mining width and different depth. The result was validated by the actual, the mining width and coal pillar width accorded with Nanding coal mine fact. The result of prediction will guide Nanding coal mine exploit safely in deep area. Keywords-water inrush from coalbed floor; strip-partial mining; permeable failure depth in the coalbed floor;mining width;coal pillar width