The mining of deep coal seams in the North China coalfields is threatened by the risk of water inrush from the Ordovician karst. As the mining depth increases, traditional methods of drainage depressurization and grouting reinforcement of the coal floor are increasingly ineffective at solving the problem of water inrush from the Ordovician karst. Grouting reinforcement of the Fengfeng Formation in the Ordovician (Ordovician top) was applied 10 years ago to solve this problem, prevalent recently, and mastering the vertical karst development is fundamental and prerequisite work. This paper carried out a study on the vertical karst development and grouting reinforcement of the Ordovician top in the Feicheng coalfield, China. Macroscopic and microscopic characteristics of the karst were researched by analysis of borehole cores and water inflow, slice identification and X-ray testing results to reveal the vertical karst development of the Ordovician top. Five layers were developed, from top to bottom: confining zone, fissure network zone, karst fissure and pore zone, karst channel zone and confining zone. Then the suitable grouting reinforcement layer was determined to be 5–45 m below the Ordovician top interface. The engineering practice of grouting reinforcement was carried out in the No. 8806 working face in the Baizhuang coal mine. The grouting technology and the evaluation of the grouting effect were analyzed comprehensively from the perspectives of the water inflow characteristics obtained from drilling and the apparent resistivity characteristics before and after grouting, which confirm the vertical karst development interpretation and good grouting effect. The study provides guidance for the prevention and control of Ordovician water disasters of the Feicheng coalfield, as well as other coal mines in North China.

中文翻译：

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肥城煤田奥陶系顶部垂向岩溶发育特征及注浆加固工程实践

奥陶系岩溶突水风险威胁着华北煤田深部煤层的开采。随着开采深度的增加，传统的排采降压和煤底板注浆加固方法对解决奥陶系岩溶突水问题的效果越来越差。奥陶系（奥陶系顶部）风峰组注浆加固是10年前解决这一问题的方法，这一问题最近普遍存在，掌握垂直岩溶发育是基础和前提工作。对肥城煤田奥陶系顶部垂直岩溶发育及注浆加固进行了研究。通过钻孔岩心和涌水量分析，研究了岩溶的宏观和微观特征，切片识别和X射线检测结果揭示奥陶系顶部垂直岩溶发育。发育五层，自上而下为：围压带、裂隙网带、岩溶裂隙和孔隙带、岩溶水道带和围压带。然后确定合适的注浆加固层位于奥陶系顶部界面以下 5-45 m。注浆加固工程实践在百庄煤矿8806工作面进行。从钻井获得的涌水特征和注浆前后的视电阻率特征等方面综合分析了注浆工艺和注浆效果评价，证实了垂直岩溶发育解释和良好的注浆效果。