Zonal Evolution Mechanism and Coupled Superposed-Arch Bearing Effect in Loose-Fragmented Soft-Rock Roadways

Abstract

To effectively address the challenge of stabilizing roadways in loose and fractured rock masses, the 12810 transportation roadway of the Yunjialing Mine was selected as the engineering case. The modified Hoek–Brown criterion was employed to derive analytical expressions for the stress distribution in different zones of the surrounding rock and for the radius of the plastic zone, thereby revealing the key factors controlling roadway stability. Based on the postexcavation degradation characteristics, the surrounding rock was divided from the excavation boundary inward into a fractured zone, a plastic softening zone, and an elastic zone, and the corresponding control principles and key techniques for extremely fractured soft-rock roadways were proposed. On this basis, three major control measures were identified: restraining the expansion of the fractured zone through high-prestress support components, mobilizing the bearing capacity of the surrounding rock through an effective support-bearing zone, and reinforcing weak sections to form a continuous bearing ring. Accordingly, a full-section combined control scheme of “high-strength prestressed long-short cables plus floor destressing anchorage” was developed. Considering the characteristics of this support scheme and based on the Hoek–Brown criterion suitable for loose and fractured rock masses, a “coupled superimposed bearing arch” capable of achieving both internal and external load bearing was proposed. This coupled bearing arch unifies the interaction between the support system and the surrounding rock with the radial confining force provided by the support, significantly amplifying the load-bearing capacity of rock bolts and cables. The results indicate that the extent of the fractured zone decreases with increasing uniaxial compressive strength and geological strength index (GSI) of the surrounding rock. Progressive expansion and transformation of the boundary between the fractured zone and the plastic softening zone is identified as the fundamental cause of large-scale rock mass fragmentation and bolt/cable anchorage failure. After applying the combined control scheme, deformation of the 12810 roadway was effectively controlled: The total convergence of the sidewalls was approximately 362 mm, roof subsidence about 142 mm, floor heave about 215 mm, and no large-scale cable ruptures occurred, ensuring roadway stability.