Clarifying intercalary rock damage laws in bifurcated small net spacing tunnels under working condition of alternate blasting excavation is helpful to better ensure onsite construction of tunnels and stability of surrounding rock. Here, the 3-D finite difference software FLAC was used to simulate alternate excavation processes of bifurcated tunnels with small net spacing under action of blasting load, and damage distribution and evolution laws of intercalary rock under different excavation conditions were mainly studied. Finally, the onsite acoustic wave damage range detection results of Xiamen Haicang Port dredging channel bifurcated tunnel project were used to verify the simulation results. The study showed that stress wave generated by blast is reflected at bifurcation to form tensile stress to make section damage at bifurcation more serious; damage of intercalary rock in tunnel reveals an asymmetric "V" distribution, and damage gradually increases from inside of intercalary rock to contour line, the maximum damage of intercalary rock at main tunnel side is in the range of 90° - 120°, and the maximum damage of intercalary rock at ramp side is in the range of 90° ; thickness of intercalary rock has a larger impact on its damage, with increase in thickness, damage degree of intercalary rock decreases and damage range does not penetrate left and right tunnels; compared with 2 m footage, the complete damage area of 5 m footage increases by 58. 5%, damage penetration area increases by 70% ; the complete damage area of 1-step offset increases 1. 27 m compared with 4-step offset, and the damage penetration range also increases to a certain extent; excavating a smaller section firstly is conducive to stability of intercalary rock, and the damage symmetry of surrounding rock is better, but rock mass damage far away from intercalary rock can expand; the numerical simulation results are basically consistent with the onsite measurement results, the simulation results can provide a certain reference for constructing bifurcated small net spacing tunnels of highway. © 2023 Chinese Vibration Engineering Society. All rights reserved.
