Geotechnical site investigation for tunneling and underground works by advanced passive surface wave survey

This study introduces crosscorrelation seismic interferometry, a new and feasible complimentary surface wave survey for geotechnical site investigation for tunneling and underground works. Crosscorrelation seismic interferometry uses ambient noise as source to estimate the green's functions received by geophones. The proposed methodology is presented and demonstrated by three case studies in Singapore. The 1st case study demonstrates the workflow of the proposed method. Conventional active multichannel analysis of surface waves (MASW) and passive microtremor array measurement (MAM) have also been carried out on the same site. The comparison with classic active MASW shows that the dispersion curves and shear wave velocity profiles derived by crosscorrelation are more comparable and reasonable. With multiple signal classification (MUSIC) beamforming, the direction of arrival (DOA) of ambient noise field can be characterized. As the prerequisite of crosscorrelation method, with the known DOA, it also affords the opportunity to measure both Rayleigh and Love waves. The 2nd case study demonstrates that the polarization of shear wave velocities can be distinguished by the proposed method. The 3rd case study shows a feasible way to construct a 2D shear wave velocity profile. In short, with a simple linear array, fewer geophones, crosscorrelation is considered to be an attractive complement to the conventional MAM and MASW survey.