Study on large deformation mechanism and control technology of layered carbonaceous slate in deep tunnels.

To address the large deformation of a layered soft rock tunnel, the Muzhailing Tunnel was selected as the research subject, and an anchor cable made of Negative Poisson's ratio steel (NPR anchor cable) was used for the tunnel support. A combined approach of laboratory experiments, numerical simulations, and field tests was utilized to analyze the deformation mechanisms of layered carbonaceous shale under high ground stress, and a support scheme with an NPR steel anchor cable was proposed. The mechanical properties of the NPR anchor cable were studied using laboratory static tensile tests. The results indicated that NPR anchor cables exhibit constant tension and uniform stretching during the stretching process, with no apparent necking phenomenon upon fracture. By establishing a DFN-DEM tunnel numerical model and simulating the deformation progression of surrounding rocks with varying joint dip angles, the large deformation mechanism of rock bending and shear slip in the Muzhailing Tunnel was elucidated. The field application tests of the NPR anchor cable validated its efficacy in controlling large deformations of the rock mass, providing new support materials and methods for large deformation support in soft rock tunnels. [ABSTRACT FROM AUTHOR]