Mechanical Behaviour of a Deep Soft Rock Large Deformation Roadway Supported by NPR Bolts: A Case Study.

A combined support scheme was proposed to address the issue of large deformation in the deep soft rock roadway at the Tangkou coal mine in Shanxi Province, China. This support scheme includes high constant resistance, elongation, and prestressed negative Poisson's ratio (NPR) bolts as the core element, along with metal mesh, shotcrete, cable, and bottom angle grouting bolt. A numerical simulation test using Flac3D was conducted to verify the feasibility of the NPR bolt-anchored soft rock roadway. In addition, a constitutive model for a rock mass supported by NPR bolts was established. The model is based on a parallel model of a generalised Kelvin body and elastic–viscous sliding body, which was used to reveal the mechanical behaviour of an NPR bolt-anchored rock mass. The results showed that the stress–strain relationship of the NPR bolt-anchored rock mass was obtained as a piecewise function consisting of the initial, slipping, and sticking stages. The stress and strain of the NPR bolt-anchored rock mass exhibit distinct patterns under different stress conditions. Specifically, when the stress remains constant, the strain of the NPR bolt-anchored rock mass increases continuously while the stress decreases in a step-like manner. On the other hand, when the stress increases linearly with time, the strain of the anchored rock mass increases linearly, while the stress of the anchorage rock mass increases slowly in a sawtooth pattern. Furthermore, a field support test fully confirmed the effective control of the NPR bolt support on the large deformations of soft rock roadways. These findings can guide further theoretical research, engineering design, and field applications of NPR bolt-anchored rock masses. Highlights: A new combined support scheme is proposed using the NPR bolt as the core. The mechanical behaviour of an NPR bolt-anchored rock mass is revealed. Both numerical simulations and field tests demonstrated that the combined support scheme effectively controls the large deformations of soft rock roadways. [ABSTRACT FROM AUTHOR]