Abstract: In view of the tunnel reconstruction and reinforcement works under complex geological conditions such as loose surrounding rock，karst fissure development and mud filling in the karst cave，the original tunnel support shall be demolished in advance，and the area to be widened shall be expanded by blasting. Through careful design of the cutting mode and charging structure in the process of blasting exca⁃ vation，reasonable arrangement of hole positions，calculation of various blasting parameters by theoretical formulas and optimization and adjustment in combination with the actual situation on site，The blasting con⁃ struction shall be carried out in blocks，and the threshold of harmful effects such as blasting vibration， shock wave and flying stone shall be checked. Finally，it is determined that for the stable surrounding rock of the emergency parking zone，the hole depth of 1.5 m and above shall be used for excavation and con⁃ struction，and the whole section shall be blasted once; For the soft rock and fault fracture zone，it is appro⁃ priate to adopt weakening loosening blasting，or carry out the blasting construction of "multi cycle and short footage" step by step，with the cyclic footage not more than 1.0 m. For the area with good surrounding rock conditions for traffic and pedestrian cross tunnels，the designed blast hole depth is 1.5 m，and the cy⁃ clic footage is 0.95~1.35 m; The depth of blast holes in the surrounding rock soft area is 1.0 ~ 1.5 m，the cyclic footage is 0.8 ~ 1.2 m，and the surrounding holes are constructed by smooth blasting. The field blast⁃ ing results show that the rock fragmentation after blasting is uniform，the blasting footage reaches the de⁃ sign value，the surrounding rock is stable，and the harmful effects of blasting are effectively controlled，which provides a reference for similar tunnel blasting expansion projects.

Key words: complex geology, tunnel reconstruction, controlled blasting, blasting vibration