Evolution Of Overlying Strata Bed Separation And Analysis Of Water Inrush Risk In Fully-Mechanized Top Coal Caving Mining Of The Ultra-Thick Coal Seam In Yonglong Mining Area

In the past decade,with the gradual increase in coal development in China and the shift of coal mining focus to the northwest region,incidents of water inrush caused by strata failure have become increasingly frequent,posing a serious threat to coal mining safety.Yonglong Mining Area in the Huanglong Coalfield,characterized by its thick coal seam,deep burial depth,and thick underlying aquifer,has become a high-risk area for water inrush accidents.Therefore,based on Yonglong Mining Area as the research background,this thesis conducted in-depth research on the evolution law of overlying strata and the water inrush risk in fully-mechanized mining of ultra-thick coal seam by employing physical simulation,numerical simulation,theoretical analysis,and literature review.The goal was to provide theoretical support for preventing and controlling water inrush accidents in the mining of ultra-thick coal seam in Yonglong Mining Area,thus ensuring coal mining safety.The research work and main achievements of the thesis are summarized as follows:Collecting and summarizing the measured data of water-conducting fracture zone height in Yonglong Mining Area,fitting the collected data information and main influencing factors by using the SPSS software,and obtaining a prediction formula applicable to the water-conducting fracture zone height in Yonglong Mining Area of Huanglong Coalfield,and verifying the accuracy of the fitting formula.The development law of the water-conducting fracture zone height was analyzed,and can be roughly divided into three stages: the initial stage,the rapid development stage,and the slow and steady stage.The evolution law of overlying strata affected by mining was comprehensively analyzed,and summarized as "four zones,three arches,and five areas." According to the post-mining distribution of overlying rock structures,the evolution law of overlying rock structures was summarized as "four zones," including a curved sinking zone,a separation zone,a fracture zone,and a collapse zone from top to bottom.According to the temporal and spatial evolution during the mining process of the overlying strata,the evolution law of the overlying strata was summarized as "three arches," including an expansion arch,a limit arch,and a moving arch of the overlying strata.According to the distribution of the overlying strata and fractures during the evolution process,the law of fracture distribution in the overlying strata was summarized as "five areas," from left to right being the vertical fracture area,the narrow separation area,the compacted area,the narrow separation area,and the vertical fracture area,which are symmetrically distributed on both sides.In the process of water inrush caused by strata failure,the stress field,pore water pressure field,and seepage field are mutually coupled.The stress distribution inside the overlying rock changes significantly when the goaf coal seam loses stability,with stress concentrating in the unstable area,causing a sudden increase in stress values in that area,resulting in the phenomenon of overlying strata separation.At the same time,underground water penetrates into the unstable area through the water-conducting fracture zone and forms a high-pressure water body,thereby increasing the pore water pressure field.The increase in rock fracture degree will increase the permeability coefficient of the rock strata and thereby affect the seepage field’s variation.These factors interact with each other,resulting in the sudden emergence of a high-pressure water body and the formation of water inrush in the overlying strata.Based on the research results,the water inrush risk of the 1012007 working face in Yuanzigou Coal Mine was evaluated,and it was concluded that it had the conditions for forming a water-conducting fracture zone and water accumulation layer,was vulnerable to the dynamic pressure,and was prone to overlying strata separation and water inrush accidents.The water-conducting fracture zone height was calculated to be 218.1 m,and the lowest water accumulation layer was 234.35 m.The maximum water inflow rate during water inrush is estimated to be 790 m ~3 /h.An overall prevention and control strategy was proposed,summarized as the five-character tactics of "exploration,prevention,dredging,drainage,and monitoring.There are 43 figures,18 tables and 93 references in this thesis.