Numerical Analysis of Strain Localization in Granular Soils by Modified Cam-Clay Model Based on Micropolar Continuum Theory

To predict strain localization behaviors of granular soils, the modified Cam-Clay (MCC) model is incorporated into the second-order cone programming optimized micropolar continuum finite-element method (mpcFEM-SOCP). Based on a cylindrical cavity expansion problem, a biaxial compression problem, and a rigid strip footing problem, the numerical analyses reveal that the nonphysical strain localization behaviors including mesh-dependency of shear band, rumpling, or bifurcation can be alleviated or even removed if mpcFEM-SOCP is implemented appropriately. Furthermore, the internal characteristic length in mpcFEM-SOCP is a macroscopic physical parameter that characterizes the microscopic response of soil particles and is utilized to model the shear band width. A comparison between mpcFEM-SOCP and discrete element method (DEM) is performed, and the analysis results disclose that the internal characteristic length is closely related to the median particle size, and the evolution trend of the local void ratio in the specimen predicted by mpcFEM-SOCP agrees well with that by DEM. A larger shear dilatancy, however, is generally simulated by the latter. Finally, in the undrained analysis of the rigid footing problem, the evolution curves of excess pore-water pressure predicted by standard finite-element method and mpcFEM-SOCP may differ to some extent, as they enable the observations on the interesting evolution behaviors of excess pore-water pressure.