Study on relationship between overburden strata migration in thick loose strata with extending upper extraction limit coal mining face and support-surrounding rock

According to increase mining upper limit in thick loose strata and thus powered support jammed phenomenon occurred in coal mining face, theoretical analy sis,FLAC3 Dnumerical simulation and site measurement were applied to analyze surrounding rock stress distribution,overburden strata migration,powered support stress a nd deformation features of No.1202( 3) coal mining face in Xieqiao Mine to improve the mining upper limit. The study result showed that influenced by seam inclination,ove rburden strata structure and size reduced coal pillar,support pressure along the face inclination,overburden strata migration and others would have asymmetric distribution features. To increase mining upper limit could make the thickness of base rock becoming lower and would be one of the key factors to influence powered support selection and safety mining of coal mining face. When the thickness ratio of bedrock was 0.1 less than the thickness ration of loose strata,the curves of the powered support workin g resistance and the roof subsidence value would have " double curve" features. When the thickness ratio of the bedrock thickness and the loose strata thickness was over 0.1,the curve was close to a linear relationship. Within the rational scope of the mining upper limit,the powered support working resistance and bedrock thickness would be in inverse ratio relationship. The paper revealed that under thick loose strata to increase mining upper limit,the asymmetry of the overburden strata migration and the influe nce to relationship between support and surrounding rock could provide references to powered support selection and surrounding rock stability control of coal mining face t 0 increase mining upper limit.