Seismic site characterization

Sponsors: Rutherford Discovery Fellowship (RSNZ), Marsden Fund (RSNZ), Natural Hazards Research Platform (NHRP), NZ Earthquake Commission (EQC)

Collaborators: Misko Cubrinovski (UC), Liam Wotherspoon (Uni Auckland), Chris McGann (UC), Brady Cox (UTexas), Russell Green (VTech), Clint Wood (UArkansas)

Postgraduate researchers: Merrick Taylor, Kelly Robinson, Ethan Thomson, David Teague

Site characterization in Christchurch: This is principally driven by the objective an improved understanding of the ground motions which have been observed in the region from the 2010-2011 Canterbury earthquakes. This work is utilizing CPT/SPT, Vs (MASW and crosshole), SWS and H/V ratios to document the characteristics of strong motion stations in Christchurch (Wotherspoon et al. 2013), as well as the development of region-specific CPT-Vs correlations (McGann et al. 2014a), which has been used to obtain a shallow shear wave velocity model for the Christchurch urban region (McGann et al. 2014b). Equivalent linear, total stress and effective stress nonlinear analyses are also being used to illustrate the responses at these sites. The results of this work will lead to an improved understanding of site response effects in Christchurch, and improved characterization of these effects via simplified site classification. The results in Christchurch will eventually be extended to other major urban areas in New Zealand.

Comparison of observed seismic CPT data and Vs computed through a Christchurch-specific CPT-Vs correlation

State characterization of soils: The state concept provides a fundamental framework for the characterization of sandy soil behaviour, considering both density and confining stress, based on the location of a soil’s state relative to one or more reference lines. We have developed probabilistic relationships for the simplified characterization of a sandy soil’s state within the state concept framework. The relationships require knowledge of conventional geotechnical characterization parameters (i.e. median particle diameter, fines content and particle shape) and in situ field data (i.e. SPT values). Analyses using the simplified state concept relationships within an elastic-plastic constitutive model illustrate that the in situ relative density is the key uncertainty in cyclic liquefaction resistance.

Simplified state characterization and liquefaction resistance sensitivity analysis

Relevant Publications:

1. Bradley BA, Cubrinovski M. Simplified probabilistic state concept characterization of sandy soils and application to liquefaction resistance assessment. Soil Dynamics and Earthquake Engineering, 2013. Vol. 48, pp 104-118.
2. Taylor, ML, Cubrinovski M, Bradley BA. Characterization of ground conditions in the Christchurch Central Business District. Australian Geomechanics Journal, 2012, Vol 47, No 4, pp.43-57.
3. Green R, Wood C, Cox B, Cubrinovski M, Wotherspoon L, Bradley BA, Algie T, Allen J, Bradshaw A, Rix G. Use of DCP and SASW tests to evaluate liquefaction potential: Predictions vs. observations during the recent New Zealand Earthquakes. Seismological Research Letters, 2011, Vol. 82 No. 6, pp 927-938.
4. Cubrinovski M, Bray JD, Taylor M, Giorgini S, Bradley BA, Wotherspoon L, Zupan J. Soil liquefaction effects in the central business district during the February 2011 Christchurch earthquake. Seismological Research Letters, 2011, Vol. 82 No. 6, pp 893-904.
1. McGann C, Bradley BA, Cubrinovski M, Taylor M, Wotherspoon L. Comparison of existing CPT-Vs correlations with Canterbury-specific seismic CPT data. New Zealand Society for Earthquake Engineering Conference. 21-23 March 2014. Auckland, New Zealand. Paper 13. 8pp.
   1. McGann CR, Bradley BA, Cubrinovski M. Shallow shear wave velocity characterization of the urban Christchurch, New Zealand region. Southern California Earthquake Centre (SCEC) Annual Meeting. 7-10 September 2014. Palm Springs, California.
   2. Wotherspoon LM, Orense RP, Bradley BA, Cox BR, Wood CM, Green RA. Soil profile characterization of Christchurch strong motion stations. New Zealand Society for Earthquake Engineering Conference. 26-28 April 2013. Christchurch, New Zealand. Paper 13. 8pp.