Study On The Water Abundance Regularity Of Deep Fracture-karst Aquifer And The Critical Evaluation Of Water Inrush From Coal Floor In Coal Mine

The present mining depth reaches about 600m and inreases 12m per year to deep part in key coal mines of eastern North China. Being the basement of coal measure strata in North China coal mine, the Ordovician fracture-karst aquifer is the baleful source of water for exploiting the Carboniferous coal bed. The coal mines that the exploitation transfers into the deep stratum will be threaten by the deep high or superhigh pressure confined water from Ordovician. Mastering the water abundance and migration regularity of deep fracture-karst aquifer is one of the basal and prerequisite works for emancipating deep coal resources and ensuring safety for exploiting the deep coal bed.The paper takesâ… exploration areas for lower-group coal bed in Xinglongzhuang and Dongtan coal mine as the researched area. The water abundance characteristic of deep Ordovician fracture-karst aquifer is exposed by the ground pumping test, dewatering test in the pit, porosity and cranny ratio testing, hydrochemical field and hydraulic field analog computation. And the method which is suitable for the deep exploitation and used for evaluating criticality of water inrush from coal floor is put forward. The main results are as follows:(1) The sedimentary facies, paleogeography and karst characteristic of the Ordovician in coal mines of eastern North China is expounded. And the modern deep karst of the Ordovician is inheriting and developing on basis of palaeokarst and the declining shallow karst. And the development form of deep Ordovician karst in coal mines of eastern North China is pore and fracture.(2) The regularity of water inrush and water burst from the karst aquifer below the coal bed is analysed in division coal field of of eastern North China. And on basis of censusing and analysing 212 examples of water inrush from floor from 17 coal mines in Jiaozuo, Zibo and Feicheng mining area, the regularity of water yield and water inrush probability decreasing following the diminishing elevation and from rising to decreasing following the diminishing elevation is put forward.(3) Controlled factors of deep karst development have been studied from three aspects, including lithology, geologic structure, hydraulic field and hychemical field. Control action will not change with depth for soluble rock, as a material base, will not change its chemical composition with depth changing. The geologic structure is the main factor effecting the water abundance of deep karst aquifer. The form mechanism of folded structure is analysed and the folded structure core is always the place of water abundance. The control action of hydraulic field and hychemical field has relation to geology structure.(4) The chemical thermodynamics method is used for distinguishing the trend of karst development in researched area on basis of systematicly analyzing hydrogeological characteristic of the Ordovician karst aquifer. The principal component analysis method is used to study the master control of the Ordovician deep karst development. The hydraulic subareas have been divided using the hychemical method and the mechanism of geology structure water mimicry.The relation between geo-stress and water abundance of fracture-karst is studied on basis of geo-stress test in researched area, and the relation formula has been obtained. The dissolution fracture expanding mechanism of deep fracture-karst aquifer is discussed. The changing geo-stress(increased burial depth) effects the fracture aperture. And the fracture aperture is the main factor for effecting the fracture expanding in deep karst.(5) The flow field and water abundance characteristic of Ordovician fracture-karst aquifer in researched area is exposed by the method of dewatering test in the pit, ground pumping test and analyzing the change of water level and water chemistry composition. A hydrogeological conceptual model of the Ordovician fracture-karst aquifer in researched area has been set up, and the groundwater flow field has been analysed. The hydrochemical analog computation has been carried out for Ordovician fracture-karst aquifer in researched area. Above all, the karstification of deep karst in researched area can be simulated.(6) Based on the water inrush coefficient Ts, the unit inflow q, an index reflecting water bearing of the aquifer, is introduced. Based on statistical analysis of a large number of examples of water inrush, the relationships between water inrush potential, water inrush coefficient, and the water-enriched properties of aquifer are further researched. The achieved laws of water inrush are discussed. And a new method for evaluating risk of floor water inrush is put forward. The method of water inrush coefficient-unit inflow method can be a supplement for evaluating water inrush coefficients. The achieved results can be provided for evaluating water inrush risk of floor in deep mining of some mining areas, in which the water-enriched properties of aquifer are not obvious but water inrush coefficient is larger. And the coefficient-unit inflow method is applied for evaluating water inrush risk from floor in deep mining of the researched area on basis of analyzing the water abundance regularity of Ordovician in researched area using the dydraulic and dychemical method. The water inflow has been calculated. Ultimately, relevant preventive measures can be drawn up. The paper has 134 maps, 41 tables, 255 refernces.