Propagation Laws and Prediction of Blasting Vibration in Mountain Highway Tunnels with Multi-Level Surrounding Rock

To achieve vibration control in tunnel blasting under complex geological conditions, clarifying the propagation laws of blasting velocities and accurately predicting blasting velocities are crucial aspects of safe blasting construction. Based on the multi-level surrounding rock and multi-scheme blasting engineering of the Houyu tunnel on the expressway, LS-DYNA was used to analyze the vibration attenuation characteristics of multi-level surrounding rock under various blasting methods. Field tests were conducted to validate the rationality of the numerical simulations. Finally, a velocity prediction model considering the influence of elevation differences was established by dimensional theory. The results show that as the blast center distance increases, the resultant velocity decays rapidly at first and then more slowly. The velocity of the surrounding rock above the tunnel in the excavated area is greater than that in the unexcavated area. There is a negative correlation between the strength grade of rock and the vibration velocity. The resultant velocities of the surrounding rock, from largest to smallest, are as follows: the reserved core soil method for step excavation, the single side drift method with right upper bench, and the single side drift method with left side drift. The attenuation rates of the resultant velocities, from largest to smallest, are as follows: the single side drift method with right upper bench, the reserved core soil method for step excavation, and the single side drift method with left side drift. When using the reserved core soil method for step excavation, the minimum safety distances for buried pipelines, building clusters, temples, and oil depots are 95, 81, 447 and 73 m, respectively. When using the single side drift method, the minimum safety distances for buried pipelines, building clusters, temples, and oil depots are 56, 72, 327 and 71 m, respectively.