Modeling large three-dimensional stress reversals in cross-anisotropic sands.

摘要

A kinematic hardening mechanism has previously been proposed to capture the behavior of soil during large stress reversals in the triaxial plane. This mechanism is modified and extended into principal stress space. It incorporates rotation and intersection of yield surfaces to produce plastic strains within the original isotropic yield locus. An existing elasto-plastic model with isotropic hardening is used as the basic framework. The new combined model preserves the behavior of the isotropic hardening model under monotonic loading conditions, and the extension from isotropic to rotational kinematic hardening under three-dimensional conditions is accomplished without introducing new material parameters.; The kinematic hardening model was developed on the assumption of isotropic behavior of soil. However, most of the geomaterials are affected by anisotropy. To enable more accurate predictions the effects of inherent anisotropy must be taken into account in the modeling formulations.; A constitutive model has been developed to capture the behavior of cross-anisotropic frictional materials. The isotropic Single Hardening Model serves as the basic framework for this model. Based on the experimental results of cross-anisotropic sands in isotropic compression tests, the principal stress coordinate system is rotated such that the model operates isotropically within the rotated framework. The initial rotation angle of the yield and plastic potential surfaces is related to the degree of initial inherent anisotropy measured in the isotropic compression test. The amount of rotation of the yield and plastic potential surfaces decreases from the initial value back to zero kisotropic state) with loading. The model incorporates thirteen parameters that can be determined from isotropic compression, drained triaxial compression and extension tests.; The cross-anisotropic model is verified by comparing the predictions with a series of true triaxial compression tests performed on dense Santa Monica Beach sand. Then the cross-anisotropic model employed with the rotational kinematic hardening mechanisms is verified by predicting true triaxial tests incorporating large three-dimensional stress reversals performed on Santa Monica Beach sand. The model is shown to capture the overall trends of the observed behavior of cross-anisotropic sands during large three-dimensional stress reversals with reasonably good accuracy within the scatter of the test results.