Experimental Investigation of Acoustic Signal Characteristics of Blockages in Highway Tunnel Drainage Pipelines Using Distributed Acoustic Sensing

This study aims to quantitatively assess blockage conditions in highway tunnel drainage pipelines using acoustic wave signals. A full-scale physical model of a drainage pipeline was constructed to simulate six blockage ratio conditions ranging from 12.5% to 75%. Distributed Acoustic Sensing (DAS) technology was employed to collect acoustic signals along the pipeline. Time-domain analysis and Fast Fourier Transform (FFT)-based frequency-domain analysis were conducted to compare the waveform amplitude and dominant frequency components between blocked and unobstructed pipeline sections. The results demonstrate a significant increase in time-domain amplitude at the blockage location, with a maximum enhancement of up to 50% compared to unobstructed sections. In the frequency domain, this phenomenon is particularly pronounced within specific dominant frequency bands (core frequency bands). For instance, the 395–405 Hz band was identified as the core band under the 50% blockage ratio condition. Furthermore, the time-domain amplitude at the blockage shows a positive correlation with the blockage ratio (12.5–75%). The comprehensive analysis indicates that the time-domain characteristics of DAS-based acoustic signals can effectively identify both the location and severity of blockages in highway tunnel drainage pipelines. This research provides fundamental data for evaluating the blockage state of tunnel drainage systems based on acoustic signatures.