The Technology And Usable Conditions' Classification Of Aquifer-Protective Mining In Shallow Sand-Bedrock-Coal Seam

Western Coalmine Area of China has the characteristic of shallow coal seam,short water source and vulnerable entironment. So aquifer-protective mining might be one key safeguarding technology that has a bearing on continuous development of Western Coalmine Area when a large scale of exploitation is in progress. Therefore, on the base of geological condition of Shendong Coalfield and the analyse of status both at home and abroad, the moving law of overlying strata & the distributing characteristic of crannies above shallow coal seam have aggregately been analyzed by means of many methods & measures, such as theoretical analyse, physical simulation, numerical calculation, three-dimensional solid-liquid coupling simulation etc. And the rationale of aquifer protective mining in shallow sand-bedrock-coal seam has been analyzed in theory. Then the linchpin & basic qualification of aquifer protective mining have been brought forward. Consequently, a preliminary suit of aquifer protective mining technology, which takes rapid advancing, rational support and partial impervious measure of working face for its core, has been formed. The useable conditions have been classified carefully. Moreover, relative technics & parameters of aquifer protective mining in shallow sand-bedrock-coal seam has been calculated and innovated, and been applied in engineering practice of aquifer protective mining successfully.Innovative achievements of this dissertation have been displayed as follows:(a) The analytical method of synthetic index with multi-factors has been selected to attempt classify the condition applied to aquifer protective mining in shallow coal seam. Height of water transmitting crannies has been selected as the synthetic index of classification. Synthetic intensity of overlying strata, mining disturbing influence & integrity of strata have been taken for primary relative factors of synthetic classifying index. Moreover, the calculative formulation of water transmitting crannies'height in long-wall & short-wall working face respectively has been derived. Then the shallow sand-bedrock-coal seam has been classified to three sorts or seven regions (i.e. secures waterproof mining section; easy mining section of long wall, moderate mining section of long wall, difficult mining section of long wall; continuous multi-rooms section of short wall, placed multi-rooms section of short wall, and single room section of short wall) by aggregate comparison among height of cranny zone, ribbon of rock and thickness of bedrock. Consequently, the classifying system of aquifer protective mining in shallow sand-bedrock-coal seam has been educed.(b) The method of defining mining velocity by seepage velocity & the model of sidestep advancing mining at open-off cut has been put forward for the first time. And new arrangement mode of short wall continuous mechanical mining working face (Continuous multi-rooms, placed multi-rooms and single room of lay-out pattern) has been innovated. And aiming at each sort character of aquifer protective mining, the technical parameters & technics of each sort condition have been educed. Consequently the technical system of aquifer protective mining in shallow sand-bedrock-coal seam has been formed. It has been shown that in long-wall working face, the rational advancing velocity of aquifer protective mining is about from 10 meters to 25 meters per day, the adjusting scope of sidestep advavcing mining at open-off cut is generally more than 200 meters, the mining height is from 4 meters to 6 meters, and the supporting force might be from 5000 kN to 8500 kN; while, in short-wall working face, the rational advancing velocity of aquifer protective mining is more than 35 meters per day, the adjusting scope of sidestep advavcing mining at open-off cut is more than 150 meters, the mining height is from 3 meters to 6 meters, and the supporting force might be from 7500 kN to 9500 kN.(c) Engineering practice of aquifer proactive mining in working faces No. 32201 & No. 12404 respectively has been done in intensive water-bearing area of Shendong Mine Area by using the classifying system & technical system of aquifer protective mining. And the aquifer protective mining in this working faces has been successful. It has been shown by observation on-site & analysis of data that pre-affected scope on overlying aquifer due to mining is commonly 20 meters, while, ground water above working face might be infiltrated down quickly. Along with the close of key rock block, water level begins to rise again after 3 days or 4 days, and recovers at the fastest velocity after from 4 days to 15 days; recovery ratio is from 0.1 to 0.3 meter per day. Water level might be driven to stable after about 50 days. Two working face has passed successfully through intensive water-bearing area of safety.