Superposed disturbance mechanism of sequential overlying strata collapse for gob-side entry retaining and corresponding control strategies

Abstract

Gob-area roof rupture movement is a key disturbance factor for gob-side entry retaining. The characteristics of gob-area sequential roof collapse of overlying strata and superposed disturbance mechanism for gob-side entry retaining are obtained via physical simulation and theoretical analysis, in which the scope of disturbed strata is enlarged from main roof to fracture zone. The experiment reveals that as a working face advances, roof strata sequentially collapse from bottom to top and produce multiple disturbances to gob-side entry retaining. Key strata among the overlying strata control each collapse. Main roof subsidence is divided into three stages: flexure subsidence prior to rupture, rotational subsidence during rupture and compressive subsidence after rupture. The amounts of deformation evident in each of the three stages are 15%, 55% and 30%, respectively. After the master stratum collapses, main roof subsidence approaches its maximum value. The final span of the key stratum determines the moment and cycling of gob-side entry retaining disturbances. Main roof subsidence influences the load on the filling wall. The sequential roof collapse of overlying strata results in fluctuations in the gob-side entry retaining deformation. Calculation formulae for the final span of the key stratum and the filling wall load are obtained via theoretical analysis. A control method for the stability of the gob-side entry retaining’s surrounding rock is proposed, which includes 3 measures: a “dual-layer” proactive anchorage support, roadside filling with dynamic strength matching and auxiliary support during disturbance. Finally, the gob-side entry retaining of the Xiaoqing mine E1403 working face is presented as an engineering case capable of verifying the validity of the research conclusions.