抄録
A constitutive model for sands is proposed incorporating the superposition of strain increments caused by three imaginary two-dimensional slip planes under the respective two principal stresses and considering the mechanism of fabric change due to cyclic shear stresses. A true triaxial apparatus which has three pairs of rigid loading plates is improved by floating a pair of loading plates in the vertical direction with counterweight, to reduce the friction between the loading plates and the specimen. Various kinds of cyclic true triaxial tests along rotational stress paths on the octahedral plane such as the Mises, the Mohr-Coulomb and the Matsuoka-Nakai criteria are analyzed by the proposed model. The analytical results indicate to agree well with the experimental values. Adding the strains due to consolidation to the abovementioned stress-strain model and considering the undrained condition of no volumetric strain increments, the undrained effective stress paths under cyclic triaxial compression and extension conditions and under a rotational stress path along the Mises criterion and analyzed. From these analytical results, the relationship between the cyclic stress ratio and the number of cycles to produce the initial liquefaction is obtained, and it explains well the experimental results. A simple method for estimating the lower limit of cyclic stress ratio leading to the initial liquefaction is also proposed on the basis of the coefficient of interparticle friction. The soil parameters necessary for these analyses can be determined by a triaxial compression test and a consolidation test.
