| In recent years,with the rapid and stable development of national economy,the extent of development for vital energy,such as petroleum and natural gas,is enhanced gradually.However,coal resources is one of the important energy which plays key role in the course of promoting economic development.With the increase of coal mining,the mining way is changed from “skip mining” into “continuous mining”,which makes continuous working face nervous and strong mining pressure.Whether the aim of safe and high efficiency mining in continuous working face can be reached is attributed to the stability of coal pillar between the working face.Thus,it is very significant to probe the causes and mine pressure characteristics of fully mechanized caving continuous face and mining roadway,to attain distribution of vertical stress in coal pillar,to establish mechanics conditions of coal pillar stability,to analyze primary factors and evolution laws of coal pillar stability.In this paper,Based on stage coal pillar of fully mechanized caving face with continuous mining in tenghui mine,the site investigation,filed measurement,labrotory experiment,numerical simulation,theoretical analysis,engineering analogy were utilized to probe the contents ahead,the primary conclusions are as fowllings:(1)Combined site investigation with engineering geological condition of tenghui mine,estimation is used to attain the type of hydraulic support that is four-column hydraulic support.The working resistance is 6000 KN.The basic parameters of continuous fully mechanized caving face can be obtained that the length is 563 m,and cut depth of coal-winning machine is 600 mm,and the caving ratio is 1 to 1.16,and the range of drawing interval is from 0.675 to 0.945,which is the important analysis basis for probing characteristics of mining pressure of fully mechanized caving face.(2)The characteristics of roof pressure at "three monitoring zones",hydraulic support force,column force and monomer column force is attained.The mine pressure characteristics of fully mechanized caving face shows that the intensive extent of mine pressure is enhanced respectively.The minimum of periodic weighting length is 6.6m while the maximum is 17.6m,and the average value is 11.88 m.The caving length is from 8.5 to 15.55 m which is in accordance with periodic weighting length.Peak location of advanced abutment pressure is 44.05 m.The working state is stable,and primary causes of high mine pressure in top monitoring zone are superimposed effect of mining-induced pressure and the low setting load.The evolution law of setting load frequency and the end of loop resistance show “normal distribution”.Working state is stable and working resistance is redundant.Superposition of mining-induced stress and weak setting load is the primary factors for intensive mine pressure at upper monitoring zone.The force in the front and behind columns is balance.The force in the front column is inferior to behind column and the force in the behind column is unobvious.The characteristics of mine pressure in “three zones” is the vital basis for analyze the characteristics of mine pressure roadway and vertical stress in coal pillar.(3)The labrotory experiment and engineering analogy were utilized to attain the physical and mechanical characteristics of coal and rock strata in working face 2-103.the results show that coal stratum is weaker and soft.Dynamic load coefficient increases gradually from top monitoring zone to bottom.Borehole stressmeter was used to monitor the vertical stress of coal pillar,the results show that the influence range of abutment pressure in coal pillar is 9m,and the vertical stress can be divided into stress-relaxed area,stress-decreasing area,and elastic core are.The distribution of vertical stress is bimodal.The charateristics of mine pressure in the double mining roadway is synchronous in time and space,however,the intension shows obvious difference affected by advance ratio,motion state of rock beam,abutment pressure and so on.Axial force curves of anchor bolt and cable shows "concave" and "convex" traits.Mine pressure of roadway and fully mechanized caving face is uniformity.Deformation and failure of surrounding rock which is generated by mining-induced effect of continuous working face.The surrounding rock can be able to sustain stability in the course of advance and recovery,and the coal pillar width can be optimized furtherly.(4)The mine pressure characteristics of roadway is obtained by analyze anchor bolt(cable)force,displacement of surrounding rock,layer separation of roof.The axial force curves of anchor bolt and cable shows "concave" and "convex" traits in two mining roadways.The degree of "concave" and "convex" at adjacent roadway is obvious higher.The characteristics of cable force and displacement of surrounding rock in haulageway is in accordance with upper monitoring zone,and the characteristics in return airway is in coherence with bottom monitoring zone,which shows the result of mine pressure is reasonable and reliable.Mine pressure of roadway and fully mechanized caving face is uniformity.Deformation and failure of surrounding rock which is generated by mining-induced effect of continuous working face.The surrounding rock can be able to sustain stability in the course of advance and recovery,and the coal pillar width can be optimized furtherly.(5)Combind with characteristics of distribution of coal stratum and Based on the catastrophe theory,functional variation principle and the elastoplastic mechanical energy principle,the total potential energy function of coal pillar with bilateral mined-out area.The consistency between principle of potential energy and equilibrium surface(the critical point of surface)in catastrophe theory is uncovered,and the correlation between principle of minimum potential energy and bifurcation equation is revealed which is the important basis for establish mechanical criteria of coal pillar.The critical,stable and unstable mechanical criteria are attained on the basis of total potential energy function.The primary factors for the stability of coal pillar is probed which is supply theoretical basis for studying evolution laws of coal pillar stability.The primary effects for stability of coal pillar include height,overlying rock load,weak plane angle,elastic and plastic zone width and stiffness ratio.With the increase of overlying rock load,the loading state is changed from stability into unstability.The coal body shows "pressure sensitivity" after unstability,which shows catastrophe.With the increases of weak plane angle,the stability of coal pillar is weaker gradually,which is in accordance with the results from labrotary experiment.With the increases of stiffness ratio K,the stability is enhanced.(6)The numerical simulation results show that the mining influence on coal pillar produced by continuous stope face has positive relationship with weak plane angle.With the increase of angle,the stability is weaker gradually,and the state of vertical stress is changed from bimodal into unimodal distribution.The extension of plastic zone is enhanced gradually,and the elastic core width is reduced.The displacement on the bilateral sides of coal pillar is elevated in different extents.The evolution characteristics have consistency with experimental and numerical results which shows the result from numerical simulation is reasonable.(7)The stability of coal pillar has positive relationship with height.With the increase of height,the mining-induced influence on coal pillar is boosted,and the capacity to resist flexural deflection is inferior gradually.The plastic zone is extended in some degree,and the peak value of vertical stress is transformed,and the elastic core width decreases.Compared with evolution characteristics of plastic zone,vertical stress and displacement comprehensively in the course of width,weak plane angle,and height of coal pillar increases,the influence on the stability of coal pillar is the lowest after continuous stope face extracted.(8)With the increase of burial depth,the stability of coal pillar is weaker gradually.The mining influence on coal pillar is enhanced and the non-plastic zone and the elastic core width are reduced.The peak stress location is transformed gradually.The displacement on roof,side,and floor is boosted in different extent.The horizontal displacement of coal pillar in the adjacent working face is larger than previous coal side,and the displacements in two sides are close gradually.(9)The numerical simulation shows that the reasonable width of coal pillar should consider the mining influence on coal pillar stability comprehensively after mining roadway excavated and continuous stope face extracted.the width of coal pillar should larger,and the reasonable range is from 15 m to 23 m.Coal resources recovery ratio is enhanced when width is 19 m.The evolution laws of stability is in accordance with thoretical result in some extent.(10)Plastic zone theory and load evaluition were used to attain theoretical result of coal pillar width which is close to numerical simulation.The more reasonable range of width is from 19 m to 21 m.The result show that the stability of surrounding rock can be ensured in the course of working face advance,and the coal resources recovery is enhanced,and the production requirements of safety and high effection is realized when width is 19 m. |
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