Relationship between Fines Content and Soil Behavior Type Index at Liquefaction Sites

This technical note presents a relationship between soil behavior type index, Ic, obtained from cone penetration testing (CPT), and soil fines content, FC, obtained from laboratory testing of samples from colocated borings. Liquefaction evaluation based on CPT testing is best informed by independent evaluation of FC and plasticity characteristics by retrieving samples from the site. However, sampling is not feasible for many projects, in which case correlations between CPT data and FC are used despite the added uncertainty. The data set used to develop the relationship is from the Next Generation Liquefaction (NGL) project and consists of 227 colocated CPT soundings and boring logs from 111 sites, and a total of 2,714 Ic-FC pairs. This global data set is larger and spans a broader range of locations and geological settings than has been considered in previous models. A model was fit to the data using linear least-squares regression following logistic transformation of the FC data, and standardization of both Ic and the transformed FC data. The model is presented in a probabilistic framework based on the computed standard deviation of the residuals. An influence of soil plasticity on model residuals was found, but PI is not included as an independent variable in the model, mainly because plasticity measurements require sampling, in which case FC should be measured directly rather than being computed from Ic.