Influence of fines content on liquefied strength of silty sands

•An equation is proposed to estimate liquefied strength of cohesionless soils.•Influence of fines content on the critical strength of sand depends on the fines type.•Compressibility and state parameter control liquefied strength of silty sand.•Fine particles affect liquefaction by altering sand fabric shearing-compressibility.•A state-compressibility ratio is suggested to evaluate soil liquefaction behavior.

Critical state soil mechanics is a useful framework to understand sand behavior. In this paper, a relationship is developed for estimating undrained critical shear strength of sands based on the critical state framework. The relationship is validated by comparison with laboratory test results and sand liquefied strength from field liquefaction failure case histories. Using this relationship, the influence of fines content on undrained critical shear strength is studied for different combinations of effective stress and density. The parametric study indicates that depending on soil void ratio, effective stress, and the shape and mineralogy of the fine particles, undrained critical strength may increase, remain the same, or decrease as the amount of fines content increases. Both the susceptibility to liquefaction and the severity of strain-softening are affected by adding fines. It is suggested that the critical state parameter is inadequate for describing the behavior of liquefiable sands and sand shearing-compressibility should be taken into account in liquefaction analysis.