Research on support system and construction methods for super-large span tunnels based on NPR compensation effect

Purpose The purpose of this study is to address the challenges associated with super-large span tunnels, which currently lack a clear definition and scientifically grounded construction methods and support system designs. To achieve this, the study aims to establish an innovative mechanical model for anchor cable compensation arches, investigate the performance of conventional versus negative Poisson's ratio (NPR) anchor cables and compare the effectiveness of different construction methods. Design/methodology/approach Based on the innovative anchor cable compensation arch mechanical model developed for super-large span tunnels, this study employs a combined methodology of theoretical analysis and numerical simulation to systematically investigate tunnel stability and support efficiency. The research design involves establishing the nonlinear relationship between the arch's bearing capacity and excavation span, formulating stability criteria and support parameter principles, and conducting comparative numerical analyses of conventional versus NPR anchor cables' performance, along with evaluating the reserved core soil and double side heading construction methods through comparative assessment. Findings The findings reveal a nonlinear negative correlation between the compensation arch's bearing capacity and the tunnel excavation span. Numerical comparisons demonstrate that NPR anchor cables significantly outperform conventional ones in enhancing support effectiveness and optimizing stress distribution in the surrounding rock. Furthermore, the reserved core soil method exhibits superior performance and broader applicability, especially in projects with limited longitudinal space, compared to the double side heading method. Research limitations/implications This study assumes the surrounding rock mass is isotropic, homogeneous and continuous, which may not fully capture the effects of joints, bedding planes or faults on local stress redistribution and deformation patterns. The critical span threshold (=16 m) and the observed advantages of NPR anchor cables are specific to Grade V granite conditions, the considered in situ stress state and the support parameters used. The conclusions should not be directly generalized to other geological environments, rock types, tunnel geometries or stress conditions without further validation. Originality/value The originality of this study lies in the establishment of an innovative mechanical model for anchor cable compensation arches that accurately captures the nonlinear negative correlation between bearing capacity and excavation span in super-large span tunnels. Its value is demonstrated through the development of a comprehensive stability evaluation framework and the numerical verification of NPR anchor cables' superior support performance, together with the identification of the reserved core soil method as the optimal construction technique for spatially constrained projects, providing scientifically grounded solutions for the design and construction of super-large span tunnels.