Abstract
The frequent and complex stress variation of surrounding rock and load transfer of the lining structure during the construction of large-span double-arch tunnels pose certain challenges to subsequent construction control. This study employs a combination of physical model and numerical simulation to investigate the mechanical response of large-span double-arch tunnels during construction, and develops relevant model testing equipment and monitoring systems to provide references for similar tunnel mechanical response studies. The results show that: (1) The displacement and deformation of tunnel structures during construction experience three stages: " Slow deformation → Rapid deformation → Convergence deformation," with the settlement deformation on the same side accounting for over 80% due to construction in the same direction. (2) During excavation, the stress variation of surrounding rock and lining structures undergoes three processes: "Stress concentration → Stress release → Stress stabilization." The horizontal load transferred by the initial support causes abrupt changes in the horizontal thrust of the partition wall, while the vertical load induces an eccentric loading effect on the partition wall towards the leading side. This eccentric loading effect reaches its maximum when the leading side's bench III is excavated to the left tunnel and decreases to a minimum and stabilizes when the excavation of the right tunnel's monitoring face is completed. (3) The influence on tunnel crown settlement is in the order of Step I> Step II > Step III, while the influence length on surrounding rock stress is in the order of Step II > Step III > Step I. Therefore, these construction steps should be closely monitored initially. (4) Due to asymmetric construction, the partition wall of the double-arch tunnel is subjected to eccentric loading from the initial support load and the overlying surrounding rock load on the leading side. This effect improves as the trailing side is excavated, but the section bending moment still exhibits a "W" shape with flatter ends. The eccentric loading effect persists, increasing the risk of lateral displacement, bending-torsion, and shear failure of the partition wall.