Study On Strata Control Fundamental Theory Of Mining Mid Full Residual Coal Above Longwall Caving Goaf

China's energy structure based on coal resources would be unchanged for a long time.And with the continuous exploitation of coal resources,the current coal reserves would not meet the demand for energy in China in the future.A low recovery rate due to the historical reasons forms a large amount of residual coal resources.They amount to about 10 billion tons in Shanxi Province only,and most of them are high quality coal resources.Therefore,residual coal mining is the key to develop the existing potential reserves,ensure the national energy supply,and is also a very complicated technical problem.This thesis studies on basic and pivotal scientific issues of the residual coal resources and ground control of mining residual coal mid compound goafs,including residual coal resources,as well as floor strata stability,strata movement and the overburden failure in the process of mining residual coal mid compound goafs.The main conclusions are as follows:In this thesis,a large number of researches and the residual coal mines underground survey are carried out.The resource amount,distribution and characteristics of residual coal resources in different periods and different regions and space-time distribution of residual coal mines are analyzed in detail.On the basis of the statistical results,the residual coal was to be classified and the concept of mining residual coal mid compound goafs was put forward.Statistics show that the average coal recovery rate of history is 34.5% in China.According to the estimation by the residual coal reserve formula,the residual coal basic reserves are of 128.61 billion tons,recoverable reserves are of 40.3 billion tons.They overall increase 30.1% of coal Reserve to Production(R/P)ratio in China.A further study found that residual coal recoverable reserves of which have an initial recovery rate less than 20% is about 27.16 billion tons,which accounts for 67.4% of all recoverable reserves and has high potential exploitation value.The coal R/P ratio would increase by an average of 95.9% in the eastern provinces and 51% in the central and western regions in China.In addition,the residual coal mines account for 65.82% of all of them in the eastern coal-producing provinces.All of these indicate that the exploitation of residual coal is of great significance to the sustainable development of the coal industry in the eastern provinces where reserves are scarce.Through the analysis and researches,it is found that the floor strata can be divided into stress-concentrated area,floor structure area and floor stable area.The floor structure area easily occur instability when the re-mining working face steps across it.There are differences between compound goafs floor and common strata structure.The compound goafs floor has characteristics of static,disturbance load causing instability and impact from goaf environmental.According to the characteristics and different strata sequence,two floor strata structure disturbance models which are the surface contact ?Disturbance Block Beam Semi-arch? model and the ?Disturbance Voussoir Beam? model were established.Based on the solution and stability analysis of the models,the rotation deformation instability and sliding instability mechanisms were revealed.Under the same rock structure strength and lumpiness situation,when disturbance load coefficient and disturbance load distribution coefficient reach the corresponding critical value and the floor rock structure occurs instability.Two models are applied to the hard rock strata with lumpiness less than 0.5 and the thick and hard fracture rock strata with lumpiness exceed 0.5.In addition,on the basis of the stability analysis of the disturbance structure model,a new method was proposed to determine the feasibility of mining residual coal above longwall caving goafs,which is based on the stability of the floor structure.Through the research on the strata subsidence theory compound goafs,multi-parameters subsurface subsidence coefficient distribution model of single coal longwall goaf was established.After verification of correctness and accuracy by data fitting,the relationships between the surface subsidence coefficient,the maximum expansion amount,buried depth,mining height and strata subsidence coefficient were discussed in detail.The form of(1-q0)/?0 is defined as the bulking deformation(B-D)factor,which is the dimensionless parameter and determines the deformation characteristics of the overlying strata.The B-D factor has a maximum range of 2.84~3.40,with an average of 3.09.On the basis of the multi-parameters subsurface subsidence coefficient distribution model,a subsurface subsidence model of mining residual coal mid upper and lower longwall caving goafs was established.After analyzing the effect of wedge pillar mining for roof and floor strata,the strata subsidence models of wedge pillars and their mining area were established.On the basis of above studies,based on the probability integral method,the strata subsidence prediction model of mining compound residual above longwall caving goafs were established,which could reflect the strata properties change after mining.Through physical simulation and numerical simulation research,the residual coal and adjacent strata fracture increase in the process of compound residual coal above longwall goafs,integrity and mechanical properties reduction were observed.The stress of pillar area mining area and the inside edge of lower longwall goaf decreases,and the central goaf and the bottom of coal pillar are stress-concentrated area.The floor of residual coal affected by its mining,and the floor strata structure occur as subsidence and the rotation.The floor strata structure stability above longwall caving goaf is the key to the safety mining compound residual coal.The subsidence of mining residual coal above longwall caving goafs presents the trends of sudden rise and slow fall,which agrees with the vertically strata subsidence regularity.The above studies provide reference for the study of related technical measures of the strata control.On the background of mining residual coal(No.7 coal seam)mid compound goafs in Baijiazhuang coalmine,mining feasibility judgment and rock strata subsidence curves were plotted by MATLAB software in terms of the field measurement and physical similar experiment results.Geophysical prospecting and drilling method were used to detect the geology of the compound goafs area.Results of detection showed that the old goafs are waterless and floor strata structures of 7 coal seam are stable.In addition,determine the working face support resistance of No.7 coal seam and 3-machine supplemental,as well as put forward the related technical advice of safe mining.