Mechanism of high-preload support based on the NPR anchor cable in layered soft rock tunnels

The control of large deformation problems in layered soft rock tunnels needs to solve urgently. The roof problem is particularly severe among the deformation issues in tunnels. This study first analyzes the asymmetric deformation modes in layered soft rock tunnels with large deformations. Subsequently, we construct a mechanical model under ideal conditions for controlling the roof of layered soft rock tunnels through high preload with the support of NPR anchor cables. The prominent roles of long and short NPR anchor cables in the support system are also analyzed. The results indicate the significance of high preload in controlling the roof of layered soft rock tunnels. The short NPR anchor cables effectively improve the integrity of the stratified soft rock layers, while the long NPR anchor cables effectively mobilize the self-bearing capacity of deep-stable rock layers. Finally, the high-preload support method with NPR anchor cables is validated to have a good effect on controlling large deformations in layered soft rock tunnels through field monitoring data.