An Insight to the Effect of Initial Static Shear Stress on the Liquefaction of Sands

The effect of initial static shear stress on cyclic behavior of sands has been the concern of many researchers for more than five decades. This study includes the results of a set of cyclic simple shear tests carried out on a uniform sand with relative densities of 20%, 40%, and 60%, under three different initial normal stresses of 50, 150, and 250 kPa. All tests were performed under constant volume condition. Results show that the behavior of sands due to initial static shear stress, is controlled by two contradictive elements: first one relates to the increasing dynamic shear modulus due to the initial static shear stress that ends in greater liquefaction resistance, and the second relates to the amount of irreversible shear strains which increases with greater value of driving shear stress and consequently reduces the liquefaction resistance. These elements form alternations in the value of Kα; being increased in some zones and decreased in others. New trends observed in the variation of liquefaction resistance due to the initial static shear stress, leaded the authors to define new parameters which can interpret the failure conditions and complexities of the behavior