Study On The Law Of Subsidence In Wugou Coal Mine By Using Solid Backfilling Mining Method

In China,pillars supporting mine roofs underneath structure,railroads,or waterbodies impose great restriction to underground coal mining.This is especially true in East China,where many underground coal mines are underneath waterbodies.It is a great challenge to many coal mines to extract coals underneath waterbodies.WuGou coal mine is located in HuaiBei of AnHui Province.It employs the longwall mining technology and is facing similar underground mining challenges.The mine is covered with a strata of loose rocks with an average depth of 275 m.At the lower part of the strata lies an aquifer with a depth of about 22 m,which is right above the shallow part of the coal seam and is a major threat of water inrush.To safely extract the coals in the shallow seam,the backfilling coal excavation technique is used to reduce the vertical distance in goaf area behind the longwall face,aiming to avoid water inrush during coal excavation,especially the water inrush risk from the fourth aquifer.The benefits of backfilling is multi-folds: increasing coal excavation yield,using less surface areas used to store mine rocks,reducing potential environment pollution to the mine surroundings,and reducing surface subsidence.As a result,backfilling saves land resources and increases the mine's economic return.This study researched and analyzed the development of the backfilling technique,its status,technologies and theories related to surface subsidence when using backfilling,as well as some practical results and experiences.Based on the geological condition of WuGou mine,its mining condition,and the mechanical characteristics of the overhauling rocks,this study analyzed the pattern of the damages to the overhauling rocks and that of surface subsidence when the backfilling technique was used in mining.Surface relocation range and angular parameters,as well as dynamic deformation parameters were obtained from surface relocation observation stations CT101 and CT103.Using the probability integral method based on the genetic algorithm,surface relocation forecasting parameters were calculated for the WuGou mine using the backfilling technique: subsidence parameter q(0.657),horizontal relocation parameter b(0.14),the tangent of the major influence angle ?(1.73),coal excavation impact propagation angle ?(88.7 ?),and the shift of the inflection point S(-1.04m).Based on the actual mining conditions at WuGou mine,an industrial numerical simulation software was used to identify the changing patterns in surface subsidence and relocation deformation in relation to different backfilling rates.The heights of the caving zone and the water-flowing fractured zone above backfilling areas were investigated using surface drills and underground geophysical prospecting.The specific study in the CT101 longwall face using the geophysical prospecting method concluded the dynamic mechanism of the overhauling rocks above backfill areas.At the end,this study performed a comprehensive analysis of the differences in formation heights and the dynamics of the two belts in the overhauling rocks,surface subsidence patterns,and their impacts on land resources from the two common coal extraction methods of backfilling and caving.Especially,the difference in subsidencepatterns could be used to guide the use of backfilling in WuGou mine.It will also provide a technical guide for coal mining using backfilling and subsidence forecast in areas with similar geological characteristics.