Research On Rock Mass Engineering Geological Characteristics And Stability Evaluation Of Coal Goafs Underlying Railway

With the development of the economy,the underground resources mining area will become wider and wider with the resources exploited.In the railway construction,more and more railways have to cross the goaf.The coals have been repeatedly mined in time and space,and the rock mass deformations of goaf roofs are complicated.Safety and stability evaluation of coal goafs is one of the complicated geological problems.The foundation deformation of railway with different grades is different,so,the control standards for deformation in the goafs stability evaluation should also be different.At present,there is little comprehensive research on the coal goafs under railways,and there are more engineering geology problems in the operation and construction of railways,foundation stability research on complex coal goafs under railway is a relatively new topic.Therefore,it is very necessary to study the rock mass engineering geological characteristics and stability evaluation method based on the complex inclined coal goafs.This paper takes the 4?5 shallowly buried and inclined coal goafs under Dongping Railway as a case,the geological conditions,coal mining conditions,hydrogeological conditions and roof deformation characteristics of goafs are summarized,and the geological model is generalized.The comprehensive influence parameter?of groundwater on the structural plane is introduced,and the methods of determing goaf rock mass quality index GSI and mechanical parameters of disturbed rock mass are optimized.The reliable geological analysis model is established,then,the deformation laws of goafs are analyzed,and the comprehensive evaluation calculation methods of safety and stability of goaf are proposed.The allowed deformation of goafs under railway and the shallow treatment principle of multilayer goafs are determined.Compared with the measured datas,the evaluation methods are verified to be accurate.The research results in this paper improve the theory of goafs stability evaluation under railway.The main researches are shown as:(1)The influences of groundwater and rock types on structural surface conditions are not considered in the traditional GSI scoring system.The comprehensive influence factor?is introduced,which is related to the rock masses compressive strength and deformation modulus affected by groundwater,the new parameter K_SR is proposed to quantize structural surface conditions,then,according to rock mass integrity index K_v and parameter K_SR,structural characteristics and Structural surface conditions are quantized in GSI scoring system,which makes the method more accurate and reasonable in achieving water-rich and concealed rock mass.mechanical parameters.(2)The values of rock mass firmness coefficient and comprehensive friction angle achieved by traditional experience method are inexact,based on the optimized GSI quantitative analysis and Hoek-Brown(H-B)criterion,optimized methods are proposed to achieve rock firmness coefficient and comprehensive internal friction angle.(3)The ground surface deformation of goafs is affected by the thickness of the roof,the lithology of the rock mass,and repeated mining.Coal re-mining can aggravate the destruction and reduce the displacement angle of the upper roof rock mass.The displacement angle will not change significantly when the coals are re-mined more than 3 times.If the thickness of the soil is thin,the additional load on ground surface is transferred to the bedrock interface,then,it will no longer be transferred deeply,it acts on the bedrock interface as an additional load and has little effect on the deeper goaf roofs.(4)Based on the rock beam transfer theory of the goaf roof and compression deformation mechanism of the mining boundary,the optimized deformation calculation model of inclined goaf roofs under railway is established,the new calculation methods of total deformation,horizontal and inclination deformation are proposed,which provide basis for determing the reatment depth of goafs under railways.(5)According to the compared deformations between measured and theoretically calculated,the evaluation model and evaluation methods of inclined coal goafs are verified to be correct.