Study On Multi-seam Subsidence Prediction Methodology

In the past three decades,China's annual coal output has been ranked first in the world.As one of the four largest coal production and coal storage provinces in China,Inner Mongolia's coal production and recoverable coal reserves ranks first in the past five years.However,due to the longwall coal mining method and the forced-down caving roof management,the area of goaf and land subsidence is increasing year by year.Land subsidence not only causes indirect and direct loss of life and property,but also causes a series of social and ecological security problems,including further deterioration of the living environment,destruction of natural landscapes,grassland degradation and desertification.Therefore,the prediction of land subsidence caused by coal mining has important economical and social significance.This paper presents a new methodology for multi-seam subsidence prediction.This method is studied by combining GPS monitoring,Inversion of mechanical parameters of rock and soil mass overlying the goaf and FLAC^3D numerical simulation.Firstly,the ground surface subsidence is monitored by GPS technology;then,based on the GPS monitoring datas,the mechanical parameters of the rock and soil mass overlying the goaf are retrieved by combining the orthogonal test and the FLAC^3D numerical simulation software;finally,based on the inversion results,the FLAC^3D numerical simulation is used to predict the land subsidence in multi-layer goafs.Taking the Yangjiacun coal mine in Dongsheng mining district in Inner Mongolia as an example,this new methodology was used to predict the land subsidence caused by the double-layer goaf in this paper.The main research contents and results of the paper are as follows:?1?Through on-site investigation,the land subsidence in the study area mainly includes subsidence basins,fissures?including stepped faults?and sinkholes.The length of the fissures extends along the strike direction is about 50m-150m,the width is about 0.1m-2m,and the visible depth is about 40-80cm.In addition,the cracks are generally misaligned,moving relatively close to the surface at the side where the largest sinker area is located,and the sinking heights ranging from 50cm to 150cm;the width of sinkholes ranges from 0.1 to 0.5m,and the visible depth of the sinkholes is about 80cm.?2?Firstly,the surface settlement curve of 222201 working face was obtained by collating and analyzing the GPS monitoring datas.Secondly,the depth to excavated height of 222201working face is calculated,and the relationship between land subsidence and the depth to excavated height is analyzed.The study found that the depth to excavated height is roughly negatively correlated with land subsidence.Finally,combined with the orthogonal test design method,FLAC^3D numerical software was used to invert the mechanical parameters of the rock and soil mass overlying the goaf.?3?Based on the inversion of the mechanical parameters of rock and soil mass,FLAC³DD numerical simulation software was used to predict the ground subsidence in the double-layer goaf.And by calculating the depth to excavated height of coal seams in each working face,the relationship between the depth to excavated height of each coal seam and the land subsidence predicted by FLAC^3D numerical simulation was analyzed.The study found that the maximum land subsidence value at the 222203 working face is 11.6m.Overall,the land subsidence caused by the second-seam of coal mining is smaller than that produced by the first-seam of coal mining.The smaller the depth to excavated height is,the larger the predicted land subsidence value is.