Mechanism and Control Methods of Roof Deformations in Gob-Side Entry Retention by Roof Cutting Under Medium-Thick Coal Seams

Abstract

In order to ensure the successful implementation of gob-side entry retention by roof cutting under medium-thickness coal seams and compound roof conditions in Guandi Coal Mine, a mechanical model was established to analyze the factors affecting the roof deformation, and the roof fracturing height and roof fracturing direction were researched by way of numerical simulation and field experiments. The theoretical analysis and numerical simulation showed that the rotation angle of the upper main roof is the main factor leading to roof deformation, that increasing the support strength in the roadway cannot reduce the roof deformation, and that the roof deformation can be effectively controlled by increasing the roof fracturing height and the fracturing direction. The results confirmed that the roof fracturing height was 7 m, the roof fracturing direction was 15°, and the charging structure was 3 + 3 + 2 + 1. The roof was strengthened using a constant resistance and large deformation anchor, a single hydraulic prop reinforcement support in the lane, and a U-shaped steel retaining gangue support. The retained entry was stable at 200 m behind the working face and can meet the demands of reuse for the next mining face.