Is increase of CRR with FC caused by an increase of liquefaction resistance or a correction for SPT-N?

Abstract

In the empirical framework of liquefaction assessment, it has been long noted an apparent increase of cyclic resistance ratio (CRR) with increased fines content (FC). However, whether this an increase is caused by increase of liquefaction resistance or a decrease of penetration resistance (SPT-N) is not clear. Therefore, this study evaluates the FC effect on the liquefaction resistance and SPT-N using a Taiwan and an international liquefaction database that includes enriched fines data. The SPT-N based hyperbolic function curves that yield to 50% of liquefaction probability are systematically derived for different FC ranges by two methods. Method 1 is the direct correction of SPT-N due to FC (i.e. reduction) in the hyperbolic model that defines the upper bound curve using the maximum N value. Method 2 is to increase SPT-N to be consistent with a higher liquefaction resistance due to FC, which is typically adopted in the liquefaction analysis. The result indicates that apparent increase of N (Method 2) is not equal to the actual reduction of N due to FC (Method 1) but reflects the change associated with increase of CRR.