Abstract: Based on a three-dimensional elastoplastic constitutive model. for overconsolidated clays, an acoustic tensor and discriminator of bifurcation for strain localization under partially drained conditions are given. The analytical and numerical solutions to the model along different stress paths are resolved. The theoretical analysis shows that, there is no bifurcation occurring at the Lode angles of -30°, 15°and 30° for both single-phase and soil-water coupling two-phase materials. At the Lode angle of 0°, the bifurcation occurs for the single-phase and doesn’t occur for the soil-water coupling under undrained condition; while whether bifurcation occurs is related to the parameter under partially drained condition. There is bifurcation occurring at the Lode angle of -15° for both the single-phase and soil-water coupling. Numerical simulations on a cubic specimen for the bifurcation for the single-phase and soil-water coupling are carried out by use of a nonlinear finite element analysis software ABAQUS with the model being implemented. The numerical analysis shows that, there is no bifurcation occurring at the Lode angles of 30° for both single-phase and soil-water coupling. At the Lode angle of 15°, bifurcation occurs for the single-phase and doesn’t occur for the soil-water coupling under undrained condition; while the time when bifurcation occurs is related to the permeability under partially drained condition. There is bifurcation occurring at the Lode angles of -15° and 0° for both the single-phase and soil-water coupling. Bifurcation of numerical solutions is more likely to occur than that of analytical solutions along the same stress paths.

Key words: overconsolidated clay, constitutive model, partially drained condition, bifurcation, numerical simulation.