Effects of Anisotropic Consolidation and Stress Reversal on the Liquefaction Resistance of Sands and Silty Sands

Abstract

In this study, a total number of 83 undrained cyclic tests were carried out on Firoozkuh pure sand and sand-silt mixtures using cyclic triaxial apparatus. The tested specimens were subjected to both isotropic and anisotropic consolidation. The anisotropic consolidation was applied both in compression and in extension modes. The results indicate that the isotropic consolidated pure sandy samples when subjected to symmetric cyclic stresses exhibit asymmetric cyclic strains reversely, as extensional part of each cyclic strain curve is larger than compressional part. This behavior of sandy soils could be addressed to the anisotropic behavior of sands. The effect of adding silt on this deformational behavior of sandy specimens is studied too. The results indicated that this behavior disappears in silt mixed sand.

In addition, the effect of anisotropic consolidation on deformational behavior of pure sand and sand-silt mixtures was considered. The results indicate that the cyclic resistance of saturated sand to liquefaction is the function of compressional or extensional consolidation and besides, reversal of cyclic deviator stress. Anisotropic consolidation exerts an initial static deviator stress in triaxial tests. Effect of initial static shear stress on the cyclic liquefaction of sands is acknowledged in the literature and a correction factor of k is introduced to take this into account. However, shear stress reversal in the cases with presence of initial static shear stress is another factor that affects the liquefaction potential. A new coefficient called rc is introduced in this study to show degree of cyclic stress reversal. Combined effect of initial static shear stress and shear stress reversal is studied and it is shown that the correction factor for initial static shear stress k is not sufficient and stress reversal effect should also be considered for correction of cyclic resistance to liquefaction. Effect of initial shear stress and cyclic stress..