Vs-Based Evaluation of Select Liquefaction Case Histories from the 2010–2011 Canterbury Earthquake Sequence

The 2010–2011 Canterbury earthquake sequence included a number of events that triggered recurrent soil liquefaction at many locations in Christchurch, New Zealand. However, the most severe liquefaction was induced by the $M_{w}7.1$ September 4, 2010, Darfield and $M_{w}6.2$ February 22, 2011, Christchurch earthquakes. The combination of well-documented liquefaction surface manifestations during multiple events, densely recorded ground motions during these events, and detailed subsurface characterization information at the selected sites provides an unprecedented opportunity to add quality case histories to the empirical soil liquefaction database. The authors have already documented and published 50 high-quality liquefaction case histories from these earthquakes using cone penetration test (CPT) data. This paper examines 46 of these case histories using shear-wave velocity (Vs) profiles derived from surface wave (SW) methods and a Christchurch-specific Vs correlation based on CPT tip resistance. The Vs profiles have been used to evaluate the two most commonly used Vs-based simplified liquefaction evaluation procedures (i.e., Andrus and Stokoe and Kayen et al.). An error index ($E_I$) has been used to quantify the overall performance of these two procedures in relation to liquefaction observations. Although the two procedures are essentially equivalent for sites with normalized Vs (i.e., Vs1) $<180\mathrm{m}/\mathrm{s}$, the Kayen et al. procedure, with 15% probability of liquefaction, provides better predictions of liquefaction triggering for sites with Vs1 greater than $180\mathrm{m}/\mathrm{s}$. Additionally, total $E_I$ values obtained using Vs profiles from surface wave testing in conjunction with the Kayen et al. procedure are lower than two other CPT-based triggering procedures but higher than the total $E_I$ value obtained using the Idriss and Boulanger CPT-based procedure.