Long-term monitoring of blasting vibration for overlapping tunnels in complex conditions: case study of a new tunnel above

Abstract Vibration monitoring is key to ensuring adjacent structure safety during drill-and-blast tunneling. Previous research has seldom documented cases where new tunnels overlap above existing ones during blasting operations. To ensure the stability of both surface structures and the underlying existing tunnels during the construction of new overlapping tunnels, this study utilized equivalent load method modeling to predict vibration attenuation patterns. Based on these predictions, a monitoring scheme targeting high-risk vibration points was developed. Long-term vibration monitoring has confirmed the feasibility of this approach. Results show: (1) Simulation indicates that during new tunnel blasting, vibration amplitudes decrease with increasing blast-center distance at monitoring points. At equal blast-center distances, surface vibrations are stronger than those in the underlying tunnel. As excavation advances, anomalous vibration velocity amplification occurs both in surface ground behind the face and in the underground tunnel. These findings can guide the rational placement of monitoring points. (2) Actual monitoring data confirms vibration velocities comply with limits. Different attenuation curves are recommended for vibrations propagating downward (to subway tunnel) and upward (to surface). Vibration velocities were categorized and fitted according to site and distance characteristics, yielding two sets of site coefficients K and attenuation coefficients α . For the ZDK150-YDK150 monitoring points located underground ahead of the face, K = 153.16 and α = 1.9; for the Lanjian Hotel monitoring points located at the surface, K = 1522.33 and α = 2.05. (3) Blasting vibration dominant frequencies primarily range 20–90 Hz, exceeding most civil buildings′ natural frequencies. The frequency tends to decrease from the near-field to the far-field of the blast, with greater near-field fluctuation. The proposed ‘hazard-point locking at both ends’ monitoring layout and the ‘multiple measurements at a single point’ analysis approach can save monitoring costs and provide reference for similar projects.