Evolution of deviatoric stress and control of surrounding rock at gob side entry retaining with narrow flexible formwork wall

In order to study the distribution and evolution law of deviatoric stress of surrounding rock at gob-side entry retaining under the filling of flexible-formwork concrete wall,taking the gob-side entry retaining of No.3301 working face in Hexi coal mine as an engineering background,the uniaxial compressive strength of roadside concrete filling body of gob-side entry retaining was determined by laboratory test.Deviatoric stress and plastic zone distribution and evolution law of surrounding rock at gob-side entry retaining in the mining process of the working face was studied by a combination of methods such as field research,theoretical analysis,numerical simulation and field measurements.The mechanism of asymmetric deformation and failure of surrounding rock of gob-side entry retaining under the mining and disturbance of the working face was revealed.The numerical simulation results show that the evolutional sequence of deviatoric stress distribution of gob-side entry retaining is symmetric ellipse,asymmetric circle,narrow “strip”,wide “strip” as the working face moves forward.The plastic zone presents a dynamic response characteristic of zonal expansion.And the obvious influence zone of the roof,the bottom and the two walls of the roadway in the advanced and the lag mining areas was determined.The asymmetrically distributed “stripe” deviatoric stress peak zone shows a trend of evolution from the mining side to the solid coal side.Based on the distribution and evolution laws of deviatoric stress and plastic zone of surrounding rock of gob-side entry retaining during the mining of working face,the surrounding rock was divided into two areas with the boundary of the peak of deviatoric stress and the contour of plastic zone.According to the different support of surrounding rock of gob-side entry retaining,it was also divided into the solid coal side (A),the roadway roof (B),and the flexible-formwork concrete wall (C).The zonal asymmetric coupling control technology was proposed and applied in the field test,which was named the narrow flexible-formwork wall reinforced with cable and iron plate along single-pillar wall+strong double-row single-pillar in the roadway+high-strength and high-preloading asymmetric anchor cable in solid coal and the roof of gob-side entry retaining.