A number of undrained cyclic tests were conducted using triaxial apparatus. Firoozkooh sand was used in this investigation. Cyclic triaxial tests were done using a computerized bishop-Wesley stress path machine. In these tests, initial anisotropic consolidation was applied to the soil samples and cyclic deviator stress was applied in both compression and extension manners. The tendency to dilation in smaller horizontal to vertical initial effective stress ratio (k′) under compression mode and contraction in larger k′ in extension mode was observed clearly in terms of different number of cycles causing liquefaction. The stress-strain behavior and stress path diagrams in both extension and compression tests show a considerable difference in the mechanism of the liquefaction behavior. The effect of stress reversal ratio in the CSR-logN diagram has been studied either. Reversal ratio is introduced by the reversal coefficient (rc), which is the relative value of positive (Compress ional) portion of applied cyclic shear stress to the whole domain of shear stress. As it was observed in the tests the larger the rc, the higher was the curve in the CSR-logN diagram.
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