Investigating Steel Honeycomb Structure as Yielding Support Element for Tunnelling in Uneven Squeezing Ground

The yielding supports have been successfully used as a viable support solution in squeezing tunnels. When the lithological distribution of the formation exhibits non-uniformity, the stress on the yielding support becomes complicated and the yielding elements need to withstand not only axial compressive stress but also transverse shear stress. However, the design of previous yielding elements has often neglected consideration of the transverse shear force. To make yielding supports more suitable for tunnels in uneven squeezing ground, a honeycomb structure as yielding element is proposed due to excellent energy absorption and shear resistance. In this study, the mechanical response of honeycomb element is simulated by an equivalent orthotropic model, the plastic stage of honeycomb element is simulated by stiffness degradation method, and the mechanical characteristic parameters of the equivalent model are calculated by theoretical formula. Several numerical analyses are conducted to investigate the applicability of the honeycomb structure as a yielding element and to determine the optimal design size of the honeycomb element in uneven squeezing tunnels. According to the numerical simulation results, the honeycomb element can effectively resist transverse shear load whilst satisfying axial compression deformation. The use of honeycomb elements enhances the deformation capacity of the primary lining, significantly reduces internal compressive stress and overall plastic zone of the primary lining. The aspect ratio of the honeycomb element significantly influences the stress on the yielding support, and the optimal aspect ratio is determined based on the total failure zone of the lining.