Vibration Propagation and Dynamic Response of Adjacent Existing Tunnels Induced by Shield Tunneling in Hard Rock Strata

Shield tunneling in hard rock strata may generate considerable construction-induced vibration and adversely affect adjacent existing tunnels. To investigate the vibration propagation characteristics and the dynamic response of neighboring tunnels, this study combined field monitoring and DEM–FDM coupled numerical simulation based on a section of Jinan Metro Line 4. Vibration signals were monitored at the cutterhead, the segmental lining behind the cutterhead in the under-construction tunnel, and multiple segmental linings in the adjacent completed tunnel. The monitoring results showed that the vibration field was dominated by low-frequency components, with major spectral peaks below 50 Hz. Three-directional vibration monitoring was conducted, and the vertical component exhibited the most pronounced response at the monitoring points considered in the present adjacent-tunnel analysis; it was therefore selected for detailed investigation. A DEM–FDM coupled model was established and validated against field data. The effects of tunnel spacing, vibration source frequency, and vibration source amplitude on the response of the adjacent tunnel were then analyzed. The results showed that the side of the existing tunnel facing the new tunnel was the most sensitive location. Increasing tunnel spacing significantly reduced vibration transmission, and the near-side acceleration amplitude decreased by 80.29% when the spacing increased from 0.5D to 2D. The adjacent tunnel was more sensitive to low-frequency excitation. Within the investigated range, the adjacent tunnel exhibited a stronger response at lower excitation frequencies, particularly in the 2–6 Hz cases. Under small-amplitude loading, both acceleration and principal stress fluctuations increased with source amplitude.