Study On Coal Pillar Size Effect Of Principal Stress Direction

Coal pillar roadway protection has been used up to now as a conventional method to maintain roadway stability in coal mining in my country.Based on the "butterfly plastic zone theory",the formation mechanism of the deflection characteristics of the plastic zone of the surrounding rock of the roadway is studied,and the influence of the cross-sectional shape of the roadway and the properties of the surrounding rock on the deflection characteristics of the plastic zone is analyzed.Taking the 11030 transport roadway of Zhaogu No.2 Mine as the engineering background,a systematic study was carried out on the principal stress direction and the shape distribution characteristics and evolution law of the plastic zone in the mining roadway under different coal pillar sizes.On this basis,the relationship between the coal pillar size effect and the surrounding rock stability was discussed,and the damage of the surrounding rock of the roadway was verified through field detection,and the optimization scheme of supporting parameters was proposed.The main research contents and results are as follows:(1)Based on the boundary equation of the plastic zone around the circular hole under the non-hydrostatic pressure field,the cosine quartic invisible equation of the deflection angle of the principal stress direction and the polar coordinate angle is derived.On this basis,it is found that the plastic zone of the surrounding rock has deflection characteristics:When the principal stress direction is deflected,the plastic zone of the surrounding rock will deflect by the same angle;at the same time,the deflection characteristics of the plastic zone of the surrounding rock will not change due to the shape of the roadway section or the properties of the surrounding rock.(2)Taking the 1 1030 transport roadway of Zhaogu No.2 Mine as the engineering background,it is found that the distribution characteristics of the principal stress direction of the surrounding rock of the roadway are quite different under the condition of different coal pillar sizes.And with the increase of the coal pillar size,the direction of the maximum principal stress in the stress field in the surrounding rock area gradually deflects to the vertical direction.At the same time,the deflection of the maximum principal stress direction at different positions of the surrounding rock of the roadway shows different sensitivities to the coal pillar size.(3)Numerical simulation was used to further study the plastic zone of surrounding rock under different coal pillar sizes.It was found that the surrounding rock plastic zone of the mining roadway will show differentiated distribution characteristics due to different coal pillar sizes.The different sensitivities of the shape of the area to the change of the coal pillar size lead to the non-uniform deformation characteristics of the surrounding rock of the roadway,that is,the coal pillar size effect has different degrees of influence on the stability of the surrounding rock at different positions of the roadway.(4)Through field detection and verification,it was found that the non-uniform deformation characteristics of the surrounding rock of the 11030 transportation roadway were highly consistent with the distribution shape of the surrounding rock plastic zone.Based on the coal pillar size effect,the support parameters of the 11030 transportation roadway were optimized.The strength support material is used for reinforcement support,and the on-site industrial test shows that the support scheme can reduce the deformation of the surrounding rock by more than 60%,and ensure the safety and stability of the surrounding rock of the roadway.This study provides a theoretical reference for the stability control of surrounding rock in the mining roadway under the conditions of different coal pillar sizes.