Study On Safety Pillars In Fully Mechanized Caving Mining Under Thick And Loose Aquifer In Qingdong Coal Mine Of Huaibei

Huainan and Huaibei areas are important energy supply bases in East China,which are covered by huge loose water bodies.The high confined aquifer at the bottom of thick unconsolidated stratum is one of the main water-filling sources in mining.Water inrush accidents caused by mining near unconsolidated stratum often occur,especially when fully mechanized caving mining technology is adopted.Therefore,the key to ensure the safe and efficient production of mine is to predict the height of waterconducting fracture zone under thick and loose aquifer in fully mechanized top-coal caving mining and to reasonably set up safe coal and rock pillars.Taking the third mining area of Qingdong Coal Mine in Huaibei as an example,based on the analysis of the geological and hydrogeological conditions in the third mining area,the paper concludes that the third aquiclude is thicker and stable in distribution,while the fourth aquifer is thicker and less water-rich.The mining grade of water body in three mining areas is determined to be grade II.The soil-rock contact zone is divided into four types.The clay-mudstone contact zone is mainly distributed in the three mining areas,which is conducive to raising the mining upper limit.The development height of water-conducting fracture zone in the study area was measured by using surface borehole flushing fluid leakage observation method,color television imaging method and underground network parallel electrical method.Based on the data of 18 typical mines in Huainan,Huaibei and Shandong provinces,a multi-factor prediction formula for the height of water-conducting fracture zone in fully mechanized top-coal caving mining is established based on the multiple non-linear regression method.By using the software of 3DEC,the law of the development of water-conducting fracture in the base rock and in the soil-rock contact zone is simulated and analyzed,and the development law of water-conducting fracture zone in fully mechanized caving mining in the study area is comprehensively evaluated.Thickness of combined protective layer of bedrock-wind oxidation zone for waterproof and safe coal pillar is studied.Based on different types of soil-rock contact zone,a method to determine the thickness of protective layer under sand-proof coal pillar is proposed.Finally,the reasonable size of safe coal pillar is given.The research results have important basic application value for setting water-proof coal and rock pillars in fully mechanized caving mining under thick and loose aquifers,and have certain guiding significance for safe mining under thick and loose aquifers in adjacent mining areas of Huainan and Huaibei.