Stability analysis of compound bearing structure of gob-side entry retaining with large mining height

The concept of roadside compound structure is proposed through the analysis of roof movement of gob-side entry retaining under large mining height, and the stability mechanism is revealed by mechanical calculation. The results indicate that the roof load is born by a compound bearing structure composed of “roof-wall-floor”. The action relations of staged wall strength and roof movement are distinguished, the initial strength should be larger than the roof load, and the final strength should adapt to the roof deformation, so that the wall strength and roof movement can maintain a dynamic coordination. The roofs impose higher horizontal force on the wall under large mining height, thus the horizontal sliding factor should be less than the friction coefficient on the contact surface of wall and rock to realize self-stabilization. The inboard stress cannot be higher than the strength of roof and floor in order to avoid the strata being cut off, and the outboard stress cannot be higher than the strength of wall in order to avoid the wall being broken. Decreasing the widths of entry and wall can reduce the stress of wall, based on which the determination methods for the widths of entry and backfill body are proposed. A field test with 4.2 m mining height, whose entry and backfill width is designed to be 3 m and 4 m respectively, is conducted to demonstrate the effectiveness of the proposed method. The results verify the reasonableness of the conclusions.