Field investigation of vibration–acoustic coupling and noise prediction in urban tunnel blasting beneath high-rise buildings

Identifying the source of urban noise generated by underground tunnel blasting is essential for reliable environmental assessment. Field tests were conducted in the Kunming Metro Line 1 project, China. Three-component vibration velocity and sound pressure signals were synchronously recorded on the ground surface and at different floors of a 12F building. Continuous wavelet transforms, normalized power spectral densities, coherence and phase-delay analyses, narrow-band Hilbert envelopes, and polarization analysis were combined to distinguish blast-input characteristics, structural modal responses, and vibration–sound coupling, and to identify the contribution of vibration to noise. The results show that vibration levels generally satisfied the particle velocity limit of GB 6722, whereas both ground-surface and indoor A-weighted sound levels exceeded the 70 dBA limit in some records. The approximately 22 Hz comb-like spacing in the blast-input spectrum was not reproduced in the floor responses, which instead exhibited selective modal responses near 5, 10, 15, 25, and 50 Hz. Floor vibration and sound pressure showed poor coupling because their CWT and PSD features were inconsistent and their coherence was generally low. The 50 Hz band exhibited the highest apparent radiation efficiency and coincided with the principal indoor reverberation range. In contrast, ground-surface records showed strong but frequency-selective vibration–sound coupling, confirming that ground vibration is the primary source of surface noise. Among 99 records, the vertical component was identified as the radiation-effective axis in 63 cases, compared with 36 cases for the horizontal components, respectively. An impedance-scaled empirical relationship based on vertical vibration provided a practical estimate of unweighted radiated pressure, with a site-specific coefficient of Π = 1.23 . The results indicate that coherence-based noise assessments should be conducted separately for ground-surface and building responses, providing a reference for blasting design and environmental noise assessment in urban underground construction.