Control Effects of Pretensioned Partially Encapsulated Resin Bolting with Mesh Systems on Extremely Soft Coal Gateways: a Large-Scale Experimental Study

Pretensioned partially encapsulated resin bolting with mesh systems (PPERBMSs) are commonly employed in underground mines, particularly for soft coal gateways requiring immediate support. However, the behavior of bolts and reinforced coals has not been explained, and supporting schemes are determined by engineering analogy and experience. Herein, two large-scale physical models of extremely soft coal gateway sidewalls, reinforced with traditional and improved PPERBMSs, were constructed to probe the performance of pretensioned bolts and the deformation evolution of reinforced coal during roadway driving and panel extraction. Results reveal the bolting effect distribution characteristics of traditional PPERBMS. The mechanism and mode of bolts-mesh-surrounding coal system (BMSCS) instability were analyzed. The control effects of the two supporting schemes were compared, and stability-controlling principles for extremely soft coal roadways were proposed. High bolt pretension force and mesh stiffness are found to be important for improving the bearing capability of BMSCS, especially for reducing the extent of squeezing deformation and severe failure zones in shallow coals. The control method of “high-pretension-force bolts + fine mesh steel–plastic or rhombic screen + high-stiffness welded wire mesh + long bolt/cable for compensating reinforcement at key parts” is proposed to promote the formation of a supporting force interaction zone within surface and shallow coals, reduce the weakly reinforced region causing BMSCS structural instability, and improve the stability and bearing capability of the interaction zone in the bolt anchorage section. These findings are helpful for understanding the bolting effect of PPERBMSs and could provide guidelines for bolting design in soft coal roadways.