Stress Sensitivity Zoning Characteristics And Response Of Roadway Under Coal Pillar

Many residual coal pillars exist in upper parts of closed distance seam group during the process of descending coal mining,of which the floor is likely to appear high stress concentration and uneven distribution of stress space.When roadway below the coal seam vertically passes through the upper remained coal pillars,it is possible to arise large deformation of surrounding rock and impulsion pressure of other power disaster,seriously affecting the normal and efficient coal seam mining.Therefore,based on Xin Rui Colliery,combining with engineering geological conditions of close coal seam,this paper is using a combination of field research,theoretical analysis,numerical simulation,mining pressure monitoring and other means to study the evolution law of abnormal stress distribution in the floor of remained coal pillars and its influence on the stability of surrounding rock synergy law,putting forward the following coal roadway arrangement and the principle of dynamic control during the process of descending mining in closed distance seam group.The bearing stress distribution model inside coal pillar is established,and the analytical solution of bearing stress is deduced.Using “three indexes of stress”(including the concentration factor,stress rate,lateral pressure coefficient)to describe the floor surrounding rock stress state of residual bearing coal pillars,we construct abnormal stress flexible analytical model of surrounding rock in single pillar,dual pillar and pillar group,reveal the spatial distribution law and influencing area of stress concentration factor,stress rate and lateral pressure coefficient.The influencing law of “three indexes of stress” caused by the mining of lower working face is studied,the evolution law of “three indexes of stress” below goaf,below the junction between the goaf and coal pillars,below coal pillars is revealed,the design method of pillar width in the lower coal seam is put forward,and the reasonable pillar width is determined according to specific condition of Xinrui Mine.The synergy law of roadway stability affected by “three indexes of stress” is studied,we find that the concentration factor and stress changing rate inversely affect roadway stability.When the lateral pressure coefficient is less than 1,lateral pressure coefficient has less influence on roadway stability.When it is more than 1,it affects roadway surrounding rock stability inversely.High concentration factor can significantly enhance the influence that stress changing rate and lateral pressure coefficient affect roadway stability,high stress changing rate can also strengthen the influence.So we propose the concept and determination method of “three indexes of stress” in the lower coal roadway.Based on distribution and evolution law of “three indexes of stress” in the residual coal pillars,combining with the synergy law of roadway stability affected by “three indexes of stress”,a reasonable principle of lower mining roadway arrangement is put forward,lower mining roadway is divided into three types: gateroad below goaf,below the junction between the goaf and coal pillars,below coal pillars,each roadway surrounding rock control technology is determined.Research result is applied into a lower mining gateroad intersecting remained pillar with layer spacing of 3.25 m in Xinrui Mine,field investigation indicates that roadway layout and support technology effectively control the deformation of roadway surrounding rock.