A Comparative Study of Soft Rock Tunnel Control Methods Using NPR High Preload Anchor Cables: Analysis of Multiple Cases

Addressing the challenge of large deformation in soft rock tunnels is an urgent imperative. The conventional support method is mainly passive or low-stress compensation support, which proves inadequate in effectively managing the large deformation disaster of soft rock under complex geological conditions. This paper focuses on three representative soft rock tunnel scenarios characterized by slate, schist, and metamorphic rock lithologies. The primary objective is to conduct a comprehensive comparative analysis of the efficacy of the NPR (negative Poisson’s ratio effect) anchor cable high preload support system based on the excavation compensation method. The results indicate that the NPR high preload support method adeptly controls large deformation disasters in soft rock, maintaining tunnel surrounding rock deformation within 300 mm (<3%). To achieve efficient high-stress compensation through high preload, supporting technologies should be designed for different geological conditions, exemplified by the implementation of double-gradient grouting technology in the Tabaiyi tunnel. This paper comprehensively validates the effectiveness of the NPR high preload support method in mitigating large deformations in soft rock and establishes a foundation for future engineering endeavors.