Study Of Stability And Rockburst Prevention Mechanism Of Water-soaked Coal Pillar

In recent years,coal pillar type rock burst accidents occur frequently.In order to study the influence of large coal pillar soaking on rock burst,this paper takes 1314mining face which is restored to production after water inrush in Xiaoyun coal mine as the research object,from the change of softening parameters after coal pillar soaking,the change characteristics of abutment pressure in coal pillar under the influence of water immersion,the reasonable width of large coal pillar soaking and the internal fracture of large coal pillar soaking This paper systematically studies the stability of large coal pillar and the prevention and control of rock burst in the production process of working face.(1)When the production is resumed after water inrush and flooding,the softening degree of coal is different with the soaking time.With the increase of water content in coal,the strength of coal decreases gradually.When the water content in coal is supersaturated,the bearing capacity of coal is very low.Through laboratory tests,the actual mechanical parameters of coal and rock after water immersion in Xiaoyun coal mine are determined.It is concluded that water has little effect on the strength of roof rock after water inrush accident,which is related to the characteristics of water inrush accident and the permeability of rock to water.Based on the above research,it is considered that the design of wide coal pillar should be selected for the coal pillar of working face section under the characteristics of water inrush and flooding well.(2)Through the research on the influence of coal soaking,it is considered that in order to ensure the production safety of the working face,the wide coal pillar with platform shape of internal lateral abutment pressure should be selected for the design of large coal pillar with soaking.At this time,the roadway excavation is in the area of increased stress,and the support is difficult.At the same time,the leading abutment pressure in the platform shaped wide coal pillar is superimposed,and the elastic core area is always in the state of high stress.If affected by mining disturbance at this time,coal pillar rock burst accident is very likely to occur,so the stability of coal pillar is studied systematically.By establishing the mechanical model and introducing the strength formula of the plastic softening stage,the width of the softening plastic zone is calculated,and the theoretical width range of the coal pillar is finally determined.(3)The stability of coal pillar is studied by FLAC^3Dnumerical simulation.Through the adjustment of softening parameters,the distribution characteristics of lateral abutment pressure in the coal body are obtained.Based on the site of 1314working face in Xiaoyun coal mine,the roadway excavation under different width coal pillars is simulated,and the stable coal pillar range under the condition of retaining large coal pillars is obtained.Further simulation of working face mining shows that the stress change of elastic core area in different width coal pillar basically reaches a stable state at 28 m.Combined with the change of abutment pressure inside the coal pillar in the process of mining,the reasonable width of the large water soaked coal pillar in 1314 working face of Xiaoyun coal mine is determined as 28 m.(4)Through PFC simulation,the characteristics of coal pillar fracture instability under different width to height ratio and different strength conditions are studied.It is concluded that with the gradual increase of width to height ratio of the model,the more cracks develop in the model,the greater the degree of failure,the more energy released by the model failure,and the greater the energy required to achieve the failure.The wider the coal pillar is,the more instability energy is released.With the decrease of coal pillar strength,the number of cracks caused by coal pillar failure increases,the splitting failure decreases correspondingly,but the tensile failure increases.The results show that when large coal pillar is left in the working face,the coal pillar will be more stable in the process of mining,and the coal pillar is easy to produce cracks under pressure,so the energy released inside the coal pillar is more.At the same time,according to the strength change of coal pillar,the side of coal pillar which is not affected by water is more prone to accumulate energy and rock burst under the action of pressure.Therefore,it is necessary to strengthen the prevention and control of rock burst on the side not affected by water.(5)Combined with the actual monitoring results of 1314 working face in xiaxiaoyun coal mine,the stability of large coal pillar is verified from the results of microseismic activity and stress on-line monitoring.At the same time,in the process of mining,the dangerous area of the working face is divided by the seismic wave inversion,and the danger degree of the large coal pillar in the working face is verified again.Through the development of pressure relief measures in the coal pillar area,the coal pillar type rock burst in the working face is prevented.Through the inspection of the pressure relief measures taken on site,it is proved that the pressure relief effect is good,which is conducive to the prevention and control of coal pillar rock burst.This paper provides the basis for the safe mining and rock burst prevention of coal seam under the large coal pillar.