Study Of Deformation And Destruction Mechanics And Numerical Simulation On Ascending Strip Mining Of Short Distance Coal Seams

According to the viewpoint of adjacent rock equilibrium, the stratum which has definitivethickness and higher intensity is named equilibrium stratum that has such function as slowingup ground subsidence and takes a share in deformation movement of strata.Stability of coal pillar is the key factor. Based on rock mechanical experiment andnumerical simulation experiment, five bands can be distributed from edge to midst of coalpillar as survival failure region, carrying softening region, partial plasticity region, elasticityregion and original stress region, which makeup complete five-zone model.Stress arch model of ascending strip mining can be got by the association of threeelementary models of mining cover-rock roof structure. Synthesis criterion for rock layerfailure between upper coal seam and lower coal seam can be concluded with theoreticalanalysis on strip equilibrium rock layer by use of elastic-plasticity sheet theory at theassumption of intact interstratified rock layer with continuous feature and homogeneousisotropic medium. And ratio conception of width and long of workface of the upper coal seamis proposed in ascending strip mining. They are elastic criterionL_y＜(Ï€²hÏ„₀(3ξ+2)/[6(ξ+μ)γ-3Ï€²Ï„₀h])^1/2 and plastic criterion L_y＜12ξhσ_t/[γ((3ξ+1)^1/2-1)²(ξ=L_x²/L_y² is the ratio of width and long of belt workface of the upper coal seam). Ascendingstrip mining can be used on upper coal seam and interstratified rock layer don't create collapsewhile the two equations are satisfied at the meantime after mining of the lower coal seam.Numerical simulation experiment result indicates that it is necessary alignment for upper coalpillar. With stress adjustment of adjacent rock, range of yield region gradually change oversizeafter peak of support pressure and load-supporting plasticity region expanded into deep coalpillar according to analysis on Five-field model of coal pillar when coal pillars are not justified.Destabilization failure of whole upper coal pillar above mine goaf will reduce effect of stripmining because partial plasticity region expanded into coal pillar. Result of numericalsimulation indicates four key factors in ascending strip mining are definitive space length ofcoal seam, mining width of the lower coal seam, position relation of coal pillar and nature ofthe strip belt balance rock layer. Safety measure is proposed against specific engineeringexample.