Technique Of Concurrent Mining And Reclamation In Underground Mines With Multiple Coal Seams

Energe is physical base for the development of social economy.Among the proved reserve of energy resource in China,the peropotion of coal,oil and natural gas are 94%,5.4% and 0.6% respectively,which presents an obvious charateristics of rich coal,less oil,and lean natural gas.Thus,it determines the dominant position of coal in energe structure.In 2015,China produced about 3.75 billon tons of coal in 2015,which is about 47.7% of the global coal production.Though mining and utilization of coal has made a great contribution to the national economy,it also causes serious social and environmental impacts such as land subsidence,farmland production decreasing,the human-land conflict intensifing,etc.Comparatively,land subsidence seems to be one of the most prominent problems in China because 92% of the coal output comes from underground mining,with thousands of underground longwall panels.In the end of 2012,coal subsidence land has been as much as 1.56 million hectares,and expectes to expand 70 thousand annually hectares throughout China.Especially in the five coal bases with highground water table,there are many coal mines with multiple coal seams.Because of the repetitive mining of multiple coal seams,ground subsidence effect is more serious and water logged area is larger.Meanwhile the area of five coal bases is also the main agricultural production region,which called “Overlap Region”,which covers 42.7% of the total farmland in China.Hence,coal subsidence will influence more farmland after multiple coal seams mining.,and land reclamation will be more difficlut in the large-scale water logged area.All of that will deeply affected the cultivate land area and national food security.Nowadays,most of the reclamation measures were foucus on stable subsided land,which means subsidence reaches the final settlement condition after the excavation of coal.In this situation,much land already submerged into water including the fertilized topsoil,and couldn’t be cultivated.However,there are less filling materials contrasted with gaint subsidence basin.So,this kind of post-mining retreatment,will result in low percentage of farmland reclamation,poor cultivate land quality,high reclamation cost and long reclamation period.Thus,a new technology of Concurrent Mining and Reclamation(CMR)is proposed.CMR technology greatly promote the subsidence reclamation in high ground water table area,with the advantages of protecting eco-environment,higher reclaimed farmland rate,shorter reclaimed period,lower reclamation cost,full use of land,and so on.In the past of seveval year,though many research achievements have been reached on CMR,there is less research on multiple coal seams.Therefore,with the consideration of land recalamation,this study analyzed ground subsidence influences caused by mutipule coal seams mining.Then initial reclamation layout was design according to ground subsidence influences with mutipule coal seams mining.Taking the balance of earthwork in digging and filling area as the standard,optimal reclamation layout was determined.Theoretical and mathematical models of dynamic construction elevation were separately established with the analysis of influenced factors.In the end,why and how to adjust underground mining scheme were researched in considering with ground protection and reclamation.The main conclusions of this study were:(1)Carefully analyzed ground subsidence influences caused by mutipule coal seams miningIn the situation of multiple coal seams mining,the final subsidence influence is superposition of subsidence caused by different coal seams separately.So,based on different coal seams mining subsidence,final disturbed boundary,mining affect times and corresponding seam were analyzed,which showed that mining affect times and corresponding coal seams would be varied in different regions.Even if the mining affect times were same,the disturbed mining coal seams would be different.According to the diverse coal seams mining time in different regions,the whole time influenced by coal seams mining and intervals between two adjacent mining seams were studied.The resoult indicated that the mining whole time and intervals were manifold in different regions.And mining affected times and intervals would be imparity,even with the same mining whole time.Synthesize multiple coal seams mining subsidence separately,ground original topography and underground water table,water emerged time and matching mining coal seam were analyzed in detaile,which manifested that subsidence water ponded time were various in different regions,and the depth of subsidence water would increase along with the following mined coal seams.Taking Dingji coal mine in Anhui Province as a case,subsidence impacts on land use change was analyzed.The results showed that multiple coal seams minig would seriously affect regional farmland area,grain production and economic development.(2)Optimized reclamation layout for multiple coal seams mining areaBased on subsidence affections induced by for multiple coal seams mining,which included final disturbed boundary,mining affect times and corresponding seam,mining whole time,intervals between two adjacent mining seams,water emerged time and matching mining coal seam and so on,land use directions(farmland or water area)were designed preliminarily.It was also the initial lay out of filling and digging area.Considering designed elevation of stable filling area surface final subsidence condition when all coal seams were mined,cut and fill earthwork volume in filling area were analyzed in two different situations,and mathematical models of earthwork volume in filling area were constructed respectively.The soil which could get from digging area would decrease along with the mining of coal seams.So,combining diggable soil elevation and surface dynamic subsidence when reclaiming,losing soil volume in digging area were analyzed in foue reclamation situations,and mathematical models of cut earthwork volume in digging area were set up severally.Based on preliminary reclamation layout,and mathematical models of cut and fill earthwork volume in filling and digging area,reclamation layout was constantly modulated to make earthwork volume reaching a balance state without other soil and filling material,and then obtaining optimal reclamation layout.At last optimal procedure and method was presented.(3)Established theoretical and mathematical models of dynamic construction elevation for CMR in multiple coal seams mining situationIn order to guarantee reclamation effect,improve operability of construction elevation,construction elevation was divided into three phases with the consideration of concept of soil reconstruction and controlling soil erosion.The three phases of construction elevation were subsoil stacking elevation,subsoil leveling elevation and topsoil leveling elevation.In the whole elevation programmin process,there were seven influenced factors: designed elevation of stable filling area,suface subsequence sink when reclaiming,reserved earthwork in filling area,area of filling region,stacking trapezoid slope,thinckness of topsoil,looseness of topsoil and subsoil.Based on the technological thought of CMR,theoretical models for subsoil stacking elevation,subsoil leveling elevation and topsoil leveling elevation were established with the consideration of subsoil heaping shape,topsoil and subsoil looseness in different phases.It would provide scientific and reasonable guidance for field implementation.Combined with dynamic subsidence model and probability integration theory,mathematical models for subsoil stacking elevation,subsoil leveling elevation and topsoil leveling elevation were separately builded in multiple coal seams mining conditions based on the different situations for final and dynamic subsidence,which would greatly promote the widespread utilization of CMR technology for multiple coal mining area.(4)Study on requirements and method of adjusting underground mining scheme in considering ground protection and reclamationNowadays,when making underground mining scheme,there would be protective coal pillars for important buildings,waterbodys,railways,shafts and industrial sites.However,ground protection and reclamation would less be taken into account.So in order to effectively relieve contradiction between population and land,better protect precious cultivateland resources,extand land use time,ganrantee appropriate land reclamation scale,consider construction continuity and crop growing time,avoid rainy and winter season,ensure farmers’ interests,necessity of adjusting underground mining scheme was analyzed.Based on the mining theory,there are several aspects that mining scheme could be modified suitably throughout the whole development process of underground coal resources: mine field partition;stages and minig levels division;mining sequence and time for stages and minig levels;mining sequence and time for coal seams,thick seam layers and seam groups;mining shafts and laneway arrangement;working sectors segmentation;mining sequence and time for working sectors;sections and panels subdivision;mining sequence and time for panels;mining sequence and time for one panel.Combining ground protection and underground mining,the concreat adjusting methods for mining scheme were research in five different situations,which were crop ripening period;special original topography;distribution of rivers,ditches,lakes;special coal reservation condition;particular water logged situation.The methods included coordinating mining time,direction and sequence of panel,and so on.Taking Dingji coal mine in Anhui Province as a case,concrete suggestions for amending mining scheme were provided according to the exiting plan,special topography,rivers and ditches.Different subsidence impacts were contrasted between adjusted plan and the older one.The result shows that farmland could be better protected and saved,used in a longer time,which could ensure grain prosuction and minimize economic loss caused by mining subsidence.