Comparison of SPT-CPT Liquefaction Evaluations and CPT Interpretations

The NCEER liquefaction workshop document presented the Standard Penetration Test (SPT), and the newer Cone Penetration Test (CPT) methods to undertake liquefaction analyses, and discussed available data that supported the validity of their use. The workshop encouraged verification of CPT soil classification by site specific SPTs. It also stated that the two methods appear to correlate well in terms of predicting the occurrence of liquefaction. However, examination of recent case histories suggest that cyclic resistance ratios (CRR), and in turn factors of safety against liquefaction, may differ depending on the method used; in some cases by as much as ±30%. This paper examines those differences and poses the possibility that in some cases either the CPT or SPT base curves may not be conservative enough, and thus could lead to erroneous conclusions. On the issue of CPT interpretations this paper presents laboratory test results of fines content and Chinese criteria parameters of side-by-side probes for comparison with published CPT correlations.