Investigation of dynamically compacted ground by HVSR-based approach

This paper proposes a HVSR (horizontal to vertical spectral ratio)-based approach to assess a deep and dynamically compacted fill area in Western Sydney. In addition to recognizing that the predominant resonance peak of the HVSR curve is a reflection of the impedance contrast between the surface layers and bedrock, the present paper recognizes that the secondary resonance peaks of the curve at higher frequencies may reflect strong impedance contrast within surface layers. This concept has been applied to develop a methodology of HVSR-based approach relying on the measurement of the HVSR of microtremors at measuring stations, and calibration and verification by independent mechanical and MSOR (multichannel simulation with one receiver) tests. The use of MSOR tests is introduced in this paper to facilitate the calibration of the HVSR forward model, particularly in terms of providing information for the initial guess of the shear wave velocity, Vs, profile in the HVSR forward modelling. The present paper demonstrates the effective use of the HVSR-based approach to assess dynamic compaction in the gaps away from and not covered by the mechanical tests. The mapping between the depth of bedrock and the predominant resonance frequency is also extended to include the mapping of the depths of layers with strong impedance contrasts to the secondary resonance peaks, after the data have been verified by independent mechanical tests.