With the rapid development of economy and tourism, Dong Changyu tunnel which have single lane has been unable to meet the increasing traffic. Due to the terrain and geological conditions, it is unable to build a new one, there is only way to expand the existing tunnel. Based on blasting excavation of collapse cavity section, this paper analyzes rock fragmentation and blasting vibration of multi free surface. Using numerical calculation method with Lagrangian algorithm and full restart, it simulates the effect of blasting vibration on the reinforcement area of collapse cavity and the surrounding rock, and obtains vibration velocities and its law of characteristic points. Compared to the field experiments, the vibration velocities of numerical simulation are close to them. The results indicate that the numerical calculation method can descripts rock fragmentation and blasting vibration in the millisecond delay blasting. The research has reference and guidance for similar engineering.
With the rapid economic development and the increasing traffic, some old tunnels have been unable to meet the traffic demand due to low design standard and inadequate clearance. There is a development trend to rebuild and expand old tunnels. To rebuild and expand existing tunnel is more difficult than to build a new one. It should expand tunnel section, and remove the original supporting structure. The construction process is very complex, and the risk is increasing. The demolition and expansion repeatedly disturb the surrounding rock, its whole stability and the self-bearing capacity will be further reduced. If it has collapse cavity or big hole in existing tunnel, the difficulty will be even greater; more uncontrolled factors will cause greater risk of blasting construction. Therefore, the safety and stability of existing tunnel reconstruction is one of the leading research topics in geotechnical engineering.