# Calculation Method of New Assembled Corrugated Steel Initial Support Structure of Highway Tunnel
## 1 Introduction  
In recent years, China has made remarkable strides in constructing expressways in mountainous regions [1]. Numerous engineering practices demonstrate that tunnel excavation disrupts the equilibrium of initial ground stress, redistributes surrounding rock stress, and potentially leads to deformation, damage, or collapse of the surrounding rock mass. Therefore, it is essential to implement support structures to manage deformation and prevent the destruction of the surrounding rock. Current scholarly research has extensively examined the theoretical principles and deformation control technologies associated with conventional initial supports, yielding valuable insights, including stress control theories, theories on arch deformation, and bolted shotcrete arch plate support theories [2, 3, 4]. However, conventional initial supports for highway tunnels often suffer from drawbacks such as prolonged construction periods, high costs, and environmental impact. Conversely, the corrugated steel support structure offers distinct advantages, including simplified construction techniques, excellentadaptability, high stiffness, superior strength, shortened construction timelines, favorable cost-effectiveness, and exceptional durability. Corrugated steel plates (CSPs) are specialized structural elements formed by pressing standard steel plates into a corrugated profile, subsequently treated with hot galvanization and insulation processes. The corrugations typically run longitudinally along the plate, enhancing its resistance to bending by increasing the moment of inertia [5], thereby imparting greater load-bearing capacity and stability. These favorable mechanical properties and adaptable nature have facilitated their application in Highway Tunnel Engineering, particularly in Class IV-V surrounding rock strata with spans ranging from 4 to 13 m in China, demonstrating robust performance [6; 7; 8]. Scholars have extensively investigated the mechanical properties of corrugated steel lining [9] and its connection structures [10] using experiments, field monitoring, and numerical simulations. They have elucidated the failure modes of corrugated steel structures, proposed multiple methods for calculating ultimate load capacities, and validated their technical feasibility and safety reliability in practical applications [11; 12; 13]. Despite the formulation of design, manufacturing, construction, and installation guidelines and standards in various countries such as the US, Australia, and Canada [14; 15], theoretical research and engineering applications of corrugated steel have primarily been limited to open-cut engineering contexts, such as culvert construction, tunnel sheds, utility tunnels, and open trench tunnels [16; 17; 18; 19; 20; 21]. A significant research gap remains regarding using assembled corrugated steel structures in initial tunnel support. Current design methodologies, predominantly based on the ring compression design method proposed by the American Iron and Steel Institute (AISI) and Canadian highway bridge design codes, differ notably from those required for highway tunnel initial support structures, thus precluding direct application. Furthermore, the theoretical underpinnings of corrugated steel structure calculations in China are still developing, necessitating further refinement through operational condition tests and ongoing research efforts. In summary, significant gaps persist in the current research on utilizing corrugated steel structures for the initial support of highway tunnels. The absence of a standardized algorithm for simplified calculation of corrugated steel structures and an unclear understanding of how corrugated steel flange joints (CSFJs) influence the initial support structure further underscore the need for exploring calculation methods specific to this context.