A Critical State Evaluation of Fines Effect on Liquefaction Potential

Published results fi-om laboratory tests show that an increase in the percentage of fines generally leads to a reduction of the cyclic liquefaction resistance of a sand, while empirical correlations from in-situ tests consider the presence of fines as beneficial. In order to study this seemingly not univocal effect of tines content, this paper involves the integrated framework of Critical State Soil Mechanics. For this purpose, firstly the effect of tines on the location of the Critical State Line (CSL) is studied through statistical analysis of a large data set of triaxial element tests. Results show that fines affect the CSL location in the (e-lnp) space, but not its slope in (p-q) space. In particular, an increase of fines content practically leads to a clockwise rotation of the CSL in (elnp) space. Introducing this finding as a mere change in parameter values of an appropriate Critical State constitutive model, simulations of cyclic undrained triaxial tests were performed These simulations show that the presence of fines is beneficial at relatively small effective stresses, i.e. the stresses prevailing at liquefiable layers in-situ. Furthermore, these simulations show that the effect is reversed at relatively large effective stresses, i.e. the stresses usually considered in laboratory tests.