Research On Surface Subsidence Regularity And Prediction Under Composite Mediums With Different Thickness Rations Of Loose And Bedrock

A large number of mining subsidence observation practices show that subsidence regularity of coal mining rock strata and the surface does not have the same performance, the surface movement deformation values are also different and the surface damage causes larger difference under different mining conditions due to loose thickness, bedrock thickness, or thickness ratios of loose and bedrock.In this paper, based on the summarization of existing research results, sima mining area, tunliu mining area and wuyang mining area which belong to the large coal enterprise luan group are selected as experimental bases having geological features on different thickness ratios of loose and bedrock. Through lots of work such as field investigation, surface movement deformation observation, similar material physical simulation, computer numerical simulation, ground field measurement and theoretical prediction, theoretical analysis and so on, the rock strata and surface movement-deformation regularity caused by coal mining under the mining condition of composite mediums with different thickness ratios of loose and bedrock are studied and mining subsidence prediction method is presented based on thickness ratios of loose and bedrock coefficient, providing the theory basis for the prevention and recovery of coal mining damage.Innovations in the paper are as follows:(1) According to the theoretical analysis of rock strata movement, classification standards of thickness on loose and bedrock are proposed, dividing bedrock into thin bedrock and thick bedrock and also dividing loose into thin loose and thick loose.(2) According to geological mining features of mining areas in Luan, zoning study is conducted to mining conditions and different mining geological conditions are divided into three kinds:thick loose and thin bedrock (sima coal mine), thick loose and thick bedrock (tunliu coal mine), thin loose and thick bedrock (wuyang coal mine).(3) Parameters on thickness ratios of loose and bedrock are introduced for the first time. Forecasting methods on different thickness ratios of loose and bedrock soil are analyzed. The conventional probability integral method is improved. The prediction model of probability integral method containing parameters on thickness ratios of loose and bedrock is established.The main achievements and conclusions are obtained as follows:(1) According to different thickness of loose and bedrock and mining characteristics of Luan group, mining areas are divided into three types on different composite mediums with loose and bedrock:â‘ thin loose and thick bedrockâ‘¡thick loose and thin bedrockâ‘¢thick loose and thick bedrock, observations through to mining subsidence observing stations in typical feature mining areas show that:Bedrock thickness determines the duration of surface damage and the degree of surface subsidence. As medium-hard overburden rocks, the thinner of bedrock thickness, the shorter of surface movement destruction of the time; when mining depth and mining thickness are constant, loose thickness determines influence scope and destroy degree of the surface. With the increase of loose thickness, surface influence scope becomes larger, the curvature of surface horizontal deformation has also increased; (2) No matter what basic parameters or angle parameters of mining subsidence probability integral, the changes of value are closely related to thickness of loose and bedrock. The observation results show:loose thickness is thicker, subsidence coefficient is larger, and boundary angle and inflexion offset are smaller, while bedrock thickness shows opposite characteristics. So when mining depth is constant, surface movement deformation parameters and thickness ratios of loose and bedrock have close relationship.(3) Through similar material and numerical simulation analysis, it reveals the coupling deformation relationship between bedrock and loose. Since thin bedrock and thick loose, it is hard to form control layer for stopping loose substantial subsidence inside the bedrock, and loose as loads compresses bedrock, the whole overlying bedrock and loose shows integration model on loose compressed and closely followed bedrock. When the bedrock is thicker, bearing structure is shaped inside itself which controls loose role in load breakage of bedrock.(4) Rock strata movement mechanism on bedrock and loose are different, bedrock movement deformation mainly causes by spread upward through underground mining, loose movement deformation causes by its own compression through mining influence; Observation points trajectory inside the thick loose shows that bedrock with loose appears whole moving characteristic, mining influence be approximated into vertical upwards spread. The different between subsidence basins of loose and bedrock under mining influence shows:the mining degree of bedrock is higher than surface mining degree of loose, the maximum subsidence value of bedrock movement basin is lower than it of loose surface, the moving boundary of bedrock movement basin is obviously smaller than it of loose surface subsidence basin and there is significant difference in convergence.(5) Parameters on thickness ratios of loose and bedrock are proposed for the first time and introduced into probability integral method. The probability integral prediction method based on characteristics of thickness ratios of loose and bedrock is put forward. In view of characteristics on different thickness ratios of loose and bedrock, measured and prediction results are well coincident which are compared and analyzed by sima, tunliu and wangzhuang, ect.