Bounding surface hypoplasticity model for granular soils and its applications.

摘要

A comprehensive constitutive model for sand is formulated within the general framework of bounding surface hypoplasticity, and is numerically implemented. The distinctive novel feature is the dependence of the loading and plastic strain rate directions on the stress rate direction, which renders the model hypoplastic. The model can simulate different features of sand behavior under loading conditions which range from simple monotonic to complex cyclic at different amplitudes and directions. The successful simulation of the response under "rotational shear" is an important property of the model, related in practice to the phenomenon of liquefaction which may occur under cyclic loading conditions of a complex nature, entailing cyclic changes of both principal stress values and principal stress directions.; Stress ratio surfaces and a flat cap determine the loading surfaces in stress space, supplemented by a methodology to create reverse loading surfaces by a modified stress ratio concept. The mapping of the stress onto "image" stresses on loading and failure surfaces, and the dependence of plastic moduli on the distance between actual and image stresses are the basic ingredients of the bounding surface concept employed in the model formulation.; Two systematic calibration procedures of the model parameters are presented: an error minimization and a step by step calibration. Both approaches are based on closed-form analytical solutions for certain loading paths. The consistency and stability of the generalized midpoint for hypoplasticity are also studied. Numerical examples show that the implementation of the present model is successful.; Applications are made in two levels. First, simulations of laboratory tests, including rotational shear, on homogeneous soil samples are given. Second, the finite element analysis of the seafloor, subjected to wave loading, is presented. At both levels the model is shown to be superior to classical plasticity models, mainly because it captures the significant effect of the rotational shear nature of loading.