Negative Poisson’s ratio cable compensation support for 32 m super-large-span highway tunnel: A case study

Abstract

Although super-large-span tunnels ensure convenient transportation, they face many support challenges. The lack of normative construction guidance and the limited number of reference engineering cases pose a significant challenge to the stability control of super-large-span tunnels. Based on the geological conditions of a super-large-span tunnel (span = 32.17 m) at the bifurcation section of the Shenzhen interchange, this study determined support parameters via theoretical calculation, numerical simulation, and engineering analogy. The support effects of negative Poisson’s ratio (NPR) anchor cables and ordinary anchor cables on super-long-span tunnels were simulated and studied. Further, based on FLAC3D simulations, the surrounding rock stress field of NPR anchor cables was analyzed under different prestressing conditions, and the mechanism of a long-short combination, high-prestress compensation NPR anchor cable support was revealed. On the basis of numerical simulations, to our knowledge, the three-dimensional (3D) geomechanical model test of the NPR anchor cable and ordinary anchor cable support for super-large-span tunnel excavation is conducted for the first time, revealing the stress evolution law of super-large-span tunnels, deformation and failure characteristics of the surrounding rock, and the changing trend of the anchor cable’s axial force, and verifies that NPR anchor cables with high preloads are suitable for super-large-span tunnel support and have advantages over ordinary anchor cables. This study can provide a reliable theoretical reference for the support design and stability control of the surrounding rock of similar shallow-buried super-large-span tunnels.