The TBM signal is wideband and peaked between frequencies of 20 - 80 Hz. Stacking, either in frequency or time does not appear to enhance signal to noise ratios. We observe changes in spectral content associated with tunnel related activities, including the arrival and departure of the service locomotive. TBM signal atten- uation was measured for over a passband of 20-40 Hz, and is observed to decay as approximately the inverse of the squared distance between the TBM and the receivers. This is consistent with other TBM studies.
Further work will entail filtering the raw data using different passbands to try to enhance the signal out to further distances, detailed comparisons of tunnel and surface data, array analysis to determine TBM location, and analysis of spectral peaks associated with tunnel operations.
Signal and Noise Spectra |
TBM Signal Attentuation
Frequency-Wavenumber Analysis of the Mini-Array | Acoustic Resonances | Conclusions