Site characterisation by the HVSR technique

A geotechnical characterisation study of a proposed development site has been conducted using the non-invasive passive ambient noise HVSR technique. The simplicity of the HVSR technique is manifested in having a short setup time (relative to other methods), and precluding the need for any active excitation sources and external cabling. In the study a lightweight battery operated sensor was utilised to capture the prevailing ambient noise (microtremors) reflecting the structure in the ground. Microtremor measurements were taken at regularly spaced stations at the proposed development site, with each recording at a station taking no more than I 0 minutes. Thus the entire site was measured expeditiously within hours. The site characterisation involved estimating the site fundamental resonance frequency and amplification, parameters of interest in the study of a site's susceptibility to seismic activities interpreting the measured HVSR curves for a preliminary assessment of the soil layering and fitting the HVSR curves to a theoretical model to estimate the shear wave velocity (Vs) profile of the ground. Results from the HVSR technique have been verified against data from classical invasive methods (viz. borehole data and SPT). Further verification has also been made against the results from the array based MASW technique. The study suggests that the HVSR technique could be used for characterising a site in combination with a reduced number of mechanical in situ tests, and especially to fill in the gaps of the soil stratigraphy at the locations not covered by the mechanical tests.