Study On Mechanism Of Structure Of Equivalent Immediate Roof Derumpent And Surpport Load Of Large Mining Height In Fully Mechanized Mining Face Of Nearly Shallow Seam

Yushenfu mine area is one of the major coal bases in China. According to the coal seamcharacteristics the general mining method is fully-mechanized once mining all height, forrealizing high production and efficiency, large mining height in fully-mechanized methodsbecomes the trend of development, practice has shown that with the application of largemining height, there is an increasing trend of roof pressure. In order to control this kind ofroof, weighting in the support ability of increasing support in the mining area from past600t/support, increasing to800t/support, some of the hydraulic support had reached1700t/support, supporting investment soaring, face out of control exist as well. systemic study onthe roof structure and stability is needed, after height increase in shallow seam mining face.Based on national natural science fund project "Study on roof structure and stability of largemining height face in shallow seam ", integrating field measurement and statistics, physicssimulation, numerical simulation and theoretical calculation methods, dissertationinaccomplished simulation and theoretical analysis on structure of overlying strata of largemining height faces of shallow seam in mining process.The results of pressure measurement analysis and physics simulation show that: Miningheight increase, equivalent immediate roof thickened, articulation poin of the first key layerup. The definition of “equivalent immediate roof” is given according to the characteristics ofstructure of overlying strata of large mining height in fully mechanized mining face of nearlyshallow seam. Rock stratum under main roof and above coal seam which form caving zoneand take function as immediate roof names equivalent immediate roof. Structure of overlyingstrata of large mining height face of shallow seam mainly performances for double-key-layerstructure, structure of the first key layer cut falls formed meet " step voussoir beam " or "hanging arm beam" structure model, structure of the second key layer formed meet "masonrybeam" structure. the second key strata breaking distance larger, the first key strata breakingdistance smaller, face appears large and small weighting cycles.Numerical model founded based on physical simulation to make characteristic ofequivalent immediate roof fracture out. The result shows that, equivalent immediate roofderumpent is upper tensile breaking lower shear breakage. equivalent immediate roofparticipates in bearing during normal mining，broken during weighting.Reaonable canmaintai integrity of equivalent immediate roof,slow down the roof derumpent, ensure itsbetter bearing capacity.The theoretical analysis shows that the larger expansion coefficient of equivalentimmediate roof, the small revolution angle of the key block. The downward key layer may notbe able to form the hinged structure and will form the “hanging arm beam”structure whenweighting step pretty small. Stiffness of equivalent immediate roof will go down if itsthickness increase, based on comprehensive discussion of relationship of stiffness of roof andfloor, bulk modulus of hydraulic water solution, cross sectional area and hydraulic cylinderseries of column with support load,determination of support resistance formula is given.