True-Triaxial Drained Test of Tengger Desert Sand

For the lack of accurate test results in design and maintenance of desert-crossing highways in the Tengger Desert of western China, the GDS true-triaxial system was used to conduct the drained test on dense sand. Under the condition of different intermediate principal stress ratio b-value, the results showed that the stress-strain relationships in three orthogonal directions had significant differences, presenting significant anisotropy. The peak of the generalized shear stress increased with the increase of b-value. Except under the condition of b = 0, the specimen contracted firstly and then dilated, while the others dilated. The results of the different confining pressures showed that the stress-strain relationships appeared as a hardening type at low confining pressures, and as the confining pressure increased, the stress-strain relationships exhibit hardening, peaking, softening, and stable deformation characteristics. At low confining pressure, the contractive behaviors were not obvious, mainly as dilatancy, and as the confining pressure increased, the dilatancy increased gradually. The specimen transformed contract to dilatancy, and when the confining pressure reached 800 kPa, the specimen exhibited contractive behavior. The test results will provide data for subgrade design and construction in desert area.

Numerical Modeling on the Stress-Strain Behavior of Sand via Disturbed State Concept Model

The disturbed state concept (DSC), proposed by Desai, is a powerful constitutive modeling for the simulation of the material behaviors of strain hardening or softening of soil. These material parameters can be decided by the results of the triaxial compression test of soil. Some triaxial drained test were performed to obtain the deviator stress vs. axial strain behaviors of Ottawa sand with relative densities Dr ＝20% and 90% under three different confining pressures. The result shows that the experimental data and the results of the DSC model showed good correspondence. In study for disturbance parameters to effect on the curve of axial strain vs. deviator stress, it can be found that the deviator stress after peak markedly decreases when the values of disturbance parameters are reduced. The effect of disturbance parameter A on the trend for deviator stress decrease after peak is higher than that of parameter B.