Abstract: The tunnel projects in Hubei section of Zhengzhou-Wanzhou High-speed Railway represents a typical case of fully mechanized drill and blast method tunnelling in China. Characterized by large excavation area, extended advance length, and high construction efficiency, it demonstrates significant differences in mechanical behaviors and spatiotemporal effects compared to traditional small-scale mechanical partial excavation methods. Through numerical simulations and field tests, this study investigates the mechanical behaviors and spatiotemporal effects in mechanized construction of large-section tunnels. Key findings include: (1) Large-section excavation reduces face stability (40% increase in maximum pre-convergence deformation) and weakens spatial effects, making advanced support crucial for face stability control; (2) The single-stage support system with rapid closure in large-section construction effectively restrains overall settlement (22.5% reduction in final convergence deformation); (3) Under identical conditions, C30 early-high-strengh shotcrete reduces tunnel convergence deformation by 20.1% compared to C30 ordinary shotcrete, demonstrating that rapid development of high bearing capacity of support structure in early stages could effectively control deformation as spatial effects diminish and advance lengths increase.