Ken Tokeshi

Investigation of Composite Compacted Ground Using Microtremors

AbstractThis paper presents an interesting and unique case study of a composite compacted site where the upper section of dynamically compacted material achieved in the first stage of compaction was subsequently removed, reinstated, and recompacted in lifts in the second stage using conventional roller compaction. Dynamic compaction was employed initially in this area because of the need to densify deep fill materials. Although a number of mechanical methods are already available for assessing deep compaction, it has been particularly rare to find a cost-effective method that can be applied to a deep and extensive compacted site. Noninvasive techniques based on measurement of the horizontal-to-vertical spectral ratio (HVSR) of ambient vibrations (microtremors) are proposed in this paper to assist in a pilot appraisal of this area, which occupies a part of a deep and laterally extensive compacted site. First, the key features of the measured HVSR curves were interpreted to give a preliminary insight into t...

Correlation between HVSR Predominant Frequencies of Microtremor Records and Theoretical H/V Elliptical Frequencies

In the last decade, the H/V Spectral Ratio (HVSR) inversion has been explored as a low cost technique for estimating the Vs ground profile (shear wave velocity – thickness) of a site, since the HVSR curve can be obtained easily from 3 component microtremor records carried out at the ground surface. Recently, some researchers suggested that more detailed estimation of near surface layers might be inverted when the HVSR curve contains information on high predominant frequencies too. In this paper, the correlation between the experimental HVSR predominant frequencies and the minimum fundamental and/or higher mode theoretical Rayleigh H/V elliptical frequencies is discussed using available Vs ground profiles and microtremor records gathered at 19 Akita Kik-net stations in Japan. The fair correlation obtained in this case study suggests us that the assessment of theoretical Rayleigh H/V elliptical frequencies of fundamental and higher modes should be carried out to select the potential ground models before the inversion process.