Abstract: It is important to control overexcavation and underexcavation and reduce blasting disturbance to surrounding rock in blasting construction of karst tunnel. To optimize smooth blast parameters, tunnel blasting model is established with finite element software LSDYNA, and the effects of blasting parameters such as periphery hole space, resistance line size, and linear charge density on smooth blast in karst tunnel are studied. After comparing the damage thickness and equivalent stress of surrounding rock under different blasting parameters, a blasting optimization method for karst tunnel is proposed and its application in Daliangzi tunnel shows that: for the tunnel excavation with vault karst cave in grade Ⅲ limestone, if the periphery hole space is reduced from 45 cm to 40 cm, resistance line size reduced from 70 cm to 60 cm, and linear charge density adjusted from 0.150 kg/m to 0.125 kg/m, the influence of karst cave on smooth blast can be reduced, the engineering cost caused by overexcavation and underexcavation can be cut down, and the blasting disturbance to surrounding rock can be reduced, which improves the overall stability of the tunnel.

Key words: karst tunnel, smooth blast, over/under excavation, surrounding rock damage, numerical simulation, parameter optimization