Roadway Instability Mechanism of Weakly Consolidated Soft Rocks and Support Technologies

Abstract

During tunneling in weakly consolidated soft rock strata, lithology, joints, and fractures of rock strata play an important role in controlling overall roof stability of the roadway. A case study based on weakly consolidated soft rock roadway in Bojianghaizi mine was conducted to address disasters caused by sudden changes and collapse as well as difficulties in maintenance of weakly consolidated soft rock roadway. First, physical and mechanical properties of weakly consolidated soft rocks were investigated by X-ray diffraction mineral component analysis and scanning electron microscopy. Second, failure characteristics and instability mechanism of the roadway were analyzed by combining field survey and theoretical analysis. A mechanical model of fracture development on the composite roof of the roadway was built, and the initiation angle and critical stress for fracture development were deduced. The instability criteria of cracks based on cracking angle ( θ 0 ) were established. Moreover, the instability mechanism caused by roof falling was disclosed. Fractures were formed upon shear failure at vertex angle of the roadway. The fracture belt extended to the soft bedding plane of the separation stratum along the fracture propagation angle and connected with it, thereby inducing roof falling. On this basis, a high-strength and high-preload “inverted trapezoidal” anchoring mesh-beam string supporting structure + arched roadway cross-section with vertical walls + full-section guniting coupling control technology was proposed, which achieved good site application effects.