Research On Engineering Geological Properties And Stability Of The Main Coal Seam's Roof Of Jurassic System In Muchengjian Mine Of Beijing

Seam top's stability is one of the most important factors that influence coal mine's production and propping of top.With the increasing of coal seam's depth in Muchengjian coal mine,seam top's stability problem is more and more prominent so that it influences stope seriously.The coal mine has not studied seam top's stability in the past.so the study of seam top's engineering geological condition and its stability were carried out,its significance in the coal mine's production is very important.The paper's object is No.2 and No.10 seam of Jurassic system in Muchengjian coal mine,Some discipline's theory such as structural geology and rock mechanics and engineering geology were used.The study of seam top's engineering geological condition and factors influence seam top's stability were systemly carried out in seam top's sedimentary facies and lithology and lithology's combination and structure,the engineering geological styles were obtained,the seam top's stability and stability's distribution were also obtained,besed on all the analysis above,we discuss the mining effect of different rockmass's structure by FLAC^2D software.the main conclusions are as follows:(1) Jurassic coal measures strata is delta facies,the false roof's lithology is sandy mudstone,the ditect roof's lithology is siltstone and sandstone;the old roof's lithology is fine sandstone,Lithology's assioation mainly is siltstone-fine sandstone,seam roof's stability is well.(2) The main tectonic is miaoanling-zhaojishan syncline,as the result of multicycle structure,the main structure is fold and the secondary structure is faults,for these reasons,seam's occurrence is seriously transformed,seam top is very crushing and it is not intact.The seam top's stability is very bad in the situ where structure is well-developed.(3) Test result of rock's mechanics shows:the single pressure stronginess of the rock is large,siltstone's stronginess is 141.6MPa,sandy mudstone's stronginess is 165.4MPa,fine sandstone's stronginess is 213.5MPa,all these rock are hard and stable;but as the result of structures,seam top is very crushing,so its stability is become bad. (4) The result of seam top's engineering geological styles shows:the seam top's has the periodic weighting.The step distance of the periodic weighting is 15.5～22.3 meters,the periodic weighting has important influence on the stability of seam top and support.(5) Based on roof's rockmass lithological character-textural classification,the roof's stability styles can divide into four kind of types that is extremely unstable roof, unstable roof,stable roof and extremely stable roof.Stable and extremely stable roof is primarily,No.2 coal's extremely unstable and unstable roof mainly distributes east of the research area,composed 35%of entire area;No.10 coal's extremely unstable and unstable roof mainly distributes middle of the research area,composed 20%of entire area.No.2 coal's roof is less stable compared to No.10 coal's roof.(6) According to the characteristics of seam top's deposition and structure,seam top's lithological integrity layered model and fault model and fold model were establishment,and simulated the basic destroyed characteristics of different roof's rockmass which under mining effect by using the FLAC^2D software.The simulated results shows:①Under mining effect,the basic destroyed characteristic of roof's rockmass is related to roof's lithology and thickness and lithological assioation and working face's length and seam's inclination angle.②In the fault model,the stress concentration is obvious nearby the fault,When the working face has pushed the fault zone,the roof caving and crack's growth altitude to be increase,the roof's stability is bad.③In the fold model,the roof caving and crack's altitude of syncline is bigger than anticline's,and its stability is badder.④The simulated results of actual working face shows:the roof caving and crack's altitude respectively is 16.8m,33.5m,front the working surface in the 10.8～20.75m is mining effected scope,the most greatly vertical stress's concentration coefficient achieves 4.2.The simulated result is consistent with the actual situation.The factors influence seam top's stability are very many,it is necessiary to unify both the geologic and the engineering factors to evaluate roof-support-floor system's stability.