Theoretical And Experimental Study On Coal Pillar Width Retaining In Fully-mechanized Face With Large Mining Height In Shallow Coal Seam

The reasonable width of the coal pillar in the large mining height of the shallow coal seam has important engineering value and significance to ensure the stability of the roadway and improve the mining rate.In this paper,a 5-2coal seam with shallow coal seam in northern Shaanxi was taken as the engineering background,Through the combination of the field monitoring,theoretical calculation and numerical simulation,the study on the width of coal pillars in shallow mining face with shallow seam was carried out..In the field of industrial testing,and its analysis and evaluation.The main conclusions of this paper are:(1)Through the indoor test,the basic physical and mechanical parameters of coal and rock mass were obtained.The main influencing factors of the reasonable width of coal pillars in the fully mechanized coal mining face of shallow coal seam were analyzed.The stress distribution characteristics of the internal coal pillars were obtained.According to the working conditions,the force model of the coal pillar was established,and the deflection analysis of coal pillar was carried out.Based on the analysis of the working state of the coal pillar,the basic conditions for the stability of the coal pillars were obtained..(2)On the site of the original 19.2m coal pillar field monitoring showed that under the influence of primary and secondary mining,the deformation of the surrounding rock did not exceed 30 mm,the internal pillar is relatively complete,less cracks and broken areas,,and the support capacity of the pillars under the influence of mining was high,and it was necessary to optimize the width of the coal pillar.(3)Based on the theory of elasto-plastic limit equilibrium,the mechanical model wasestablished,and the vertical stress distribution of the plastic zone and the elastic zone in the coal pillar was studied according to the quadratic curve.The theoretical calculation formula of the width of the coal pillar in the working face was calculated,and the width of the pillar calculated by this formula should not be less than 15.18 m.The numerical simulation results showed that when the width of the pits was 15 ~ 17 m,the range of the plastic zone was reasonable and the width of the elastic zone were satisfactory.In summary,it was recommended to determine the width of the section of coal pillars to 15.7m.(4)On-site industrial test of coal pillars with 17.45 m after optimization,the optimized loosening range on both sides of the coal pillars was about 1.35 m and about 0.6m respectively.After optimization,the plastic zone was not more than 2m,the elastic zone width was 14.75 m,and the optimized coal pillar had sufficient stability.After optimization,the width of the pillar after 17.45 m was reasonable and feasible.