Using different state parameters for characterizing undrained static and cyclic behavior of sand with non-plastic fines

An experimental study was undertaken to identify the most suitable state index to be introduced for predicting both undrained static and cyclic strength of sand with non-plastic fines. The experimental work was based on an extensive program that includes 41 undrained monotonic triaxial compression tests and 78 cyclic simple shear tests. The respective critical state lines (CSLs) of the mixtures were used to define several state indices, namely state parameter (Ψ), pressure index (Ip) and modified state parameter (Ψm). Using the concept of equivalent granular void ratio, e*, a modified equivalent granular state parameter (Ψ*) was also introduced in terms of e*. The relationships of key features of undrained monotonic and cyclic behavior (i.e. liquefaction potential, instability stress ratio, normalized critical state resistance and cyclic liquefaction resistance) with the state indices were defined and discussed. The results showed that Ψ*, among others, could be used for characterizing and modeling both undrained static and cyclic features of tested soils more effectively. The derived correlations in terms of Ψ* appear to work very well, regardless of fines content, stress level and density state.