Deformation Mechanism of Surrounding Rock in Weakly Cemented Thick Coal Seam Roadways and Research on Graded Anchor Composite Support Technology

In the western mining areas, roadways in weakly cemented thick coal seams are highly prone to large deformations and support failures due to loose roof conditions and low cementation strength, exacerbated by stress redistribution and weathering effects. This study investigates the 11703 transportation roadway in the Dananhu No. 7 Coal Mine in Hami, Xinjiang, employing numerical simulations, theoretical analysis, and in-situ monitoring to systematically explore the deformation mechanism of surrounding rock and optimize support design. The results reveal that under excavation and weathering conditions, the roof undergoes an evolutionary process of “stress redistribution – plastic softening – interlayer separation – crushing and expansion,” eventually forming a 3.5 m deep plastic failure zone. This leads to excessive stress on the rock bolts, resulting in support failure. Moreover, the existing support system fails to establish an effective deep-shallow collaborative constraint; short bolts have insufficient control depth, while long cables do not fully mobilize their load-bearing capacity, making it difficult to restrain roof separation and deformation. To address these issues, this study proposes a Graded Anchor Composite Support Technology consisting of "surface concrete – shallow high pre-tensioned bolts – mid-depth short cables – deep long cables." The optimized scheme enhances shallow rigid constraints, increases bolt pre-tension, and strengthens mid-to-deep support, effectively confining the plastic zone and controlling surrounding rock deformation. Numerical simulations and field tests demonstrate that the optimized support system significantly suppresses plastic zone expansion, improves rock-support synergy, reduces roof subsidence by 73.3%, and decreases plastic zone depth by 40%. The research findings provide theoretical guidance and engineering reference for roadway support design under similar geological conditions.