Compression-shear behavior of high-resistance backfill walls in gob-side entry retaining for thick seams

To address the insufficient bearing capacity of roadside backfill bodies and the tilting or failure induced by uneven pressure relief of the coal seam during gob-side entry retaining in thick coal seams with hard roofs, combined compression-shear loading tests incorporating rapid resistance build-up and varying inclination angles were performed. A novel Compression Shear Coupling Test system (CSCT) was developed, and a fitted relationship between backfill width and roof subsidence was established. The strength degradation behavior of backfill specimens subjected to different shear stress components was systematically investigated. The results reveal that the peak strength of the specimens declines with increasing shear stress component, and the failure mode transitions progressively from compressive to shear-dominated failure. The high-resistance backfill material derived from this study was implemented at the N2302 gob-side entry retaining working face, accompanied by an anti-tilting design for the backfill wall. The measured roof subsidence was reduced by 59.4% relative to the theoretically predicted value, and no evident signs of failure or deterioration were observed in the backfill body. These findings provide both data support and theoretical reference for gob-side entry retaining under similar mining conditions.