The preceding companion paper presented the updating of the seismic soil liquefaction triggering relationship of Cetin et al. (2004) [1], and compared the resulting updated relationship with the earlier version. In this second paper, a detailed cross-comparison is made between three triggering relationships: (1) Seed et al. (1985) [2], as slightly updated by the NCEER Working Group (Youd et al., 2001 [3]), (2) Boulanger and Idriss (2012) [4], and (3) Cetin et al. [5]. Differences between these three triggering relationships, and the apparent causes of them are examined. Also studied are the impacts of these differences on levels of conservatism with regard to evaluation of liquefaction triggering hazard, and the resulting risks for engineering projects.

Introduction

The preceding companion paper of Cetin et al. [5] presented the updating of the seismic soil liquefaction triggering relationship of Cetin et al. [1], and compared the updated relationship with its earlier version. With the aim of developing a fair comparison framework, when compiling Cetin et al. [6] database, field case histories from relatively more recent events of 1999 Chi-Chi, 2008 Achaia-Ilia, Greece, 2010 Haiti, 2010 Chile-Maule, 2011 Tohoku, 2010–۲۰۱۱ New Zealand-Canterbury, 2012 Emilia-Romanga (Northern Italy), etc., earthquakes were excluded since they were also not included in Idriss and Boulanger [7] database. However, the presentation of a further expanded database with these additional new case histories will be the scope of another manuscript. In this second paper, a detailed cross-comparison is made between three triggering relationships: (1) Seed et al. [2] as slightly updated by the NCEER Working Group (Youd et al. [3]), (2) Boulanger and Idriss [4], and (3) Cetin et al. [5]. These three triggering relationships will be referred to hereafter as SEA1985, BI2012 and CEA2018, respectively. Differences between these three triggering relationships, and the apparent causes of these differences are examined. Also examined are the impacts of these differences on levels of conservatism with regard to evaluation of likelihood of triggering of liquefaction. Fig. 1 shows the established soil liquefaction triggering “boundary curves” associated with each of these relationships. All three relationships have been re-plotted at the same scales to make visual crosscomparisons easier and more direct. The liquefaction triggering field case history data points plotted in each figure are those of the original authors, and all data points (as well as the boundary curves) are normalized to a fines-corrected “clean sand” reference condition of N1,60,CS rather than N1,60. Plotting all three relationships on the same scale is helpful with regard to making cross-comparisons, but it can be difficult to see in detail some of the differences between the boundary curves of these three relationships. Accordingly, Fig. 2(a) shows all three studies, with the BI2012 and CEA2018 relationships represented by contours of PL = 50%, and Fig. 2(b) repeats Fig. 2(a) but with these two probabilistic relationships represented by contours of PL = 20%. The SEA1985 relationship had no probabilistic basis, so the clean sand boundary curve for that relationship remains in the same position in both figures, and serves as a useful visual point of reference. All of these curves shown in Fig. 2 are presented on a “clean sand” basis (fines content ≤ ۵%). As shown in Fig. 2, there are significant differences between the triggering boundary curves at these two important levels of hazard or probability of liquefaction.