Near surface soil characterisation by passive ambient noise HVSR method

This paper discusses the use of the passive horizontal-to-vertical spectral ratio (HVSR) ambient noise method for near surface characterisation of the soil layers at a proposed building site. The uniqueness of the HVSR method is in having no need for any external excitation sources and cabling, and the setting up time is also very short. In our study, HVSR measurements were taken at spots interspersing the few available bore logs, with each measurement taking no more than 10 minutes. This allows the entire site to be measured very expeditiously. The HVSR spectra were then inverted by fitting measured to theoretical spectra values to obtain the Vs profile of the underlying soil layers, based on an assumed layered soil model. A side benefit of this approach is that the resonance frequencies of the site were also determined without undertaking additional work. In addition to benchmarking the soil profile inverted from the HVSR measurements against the available bore log data to verify its accuracy and correctness, comparisons have also been made with the results from the MASW and ReMi array-based methods. The study shows that the HVSR method performed very well against these surface wave methods. It is thought that the HVSR technique would be especially cost-effective for characterising a large site in conjunction with a few bore logs.