Evaluation of state indices in predicting the cyclic and monotonic strength of sands with different fines contents

State parameter, ψ, has been widely used to combine the influence of void ratio, e, and stress level, p′, on the soils behavior. Stress ratio, Rs, and modified state parameter, ψm, have also been proposed for the same purpose. This paper aims to evaluate and compare the different state indices in combining the effect of fines content, density and stress level for five different types of sands, by processing a large number of previously published experimental data. The use of the recently established concept of equivalent interparticle void ratio, e⁎, in definition of the state indices is also evaluated. The results indicate that the influence of fines presence, in addition to the e and p′, on the behavior is favorably reflected by the state indices. Unique correlations were derived between the cyclic or monotonic strength and each of the state indices, independent of the fines content. The correlations, for all the different types of soils, fell into limited types of common formulations. ψ and Rs worked generally better than ψm, whether defined in terms of e or e⁎. The extension of straight part of critical state line was found to be an appropriate reference line for calculating Rs used in conjunction with e or e⁎.