真三维状态下土体强度及变形分叉影响

通过引入应力Lode角建立合理的角隅函数描述偏平面形状，对三维Mohr-Coulmb强度准则进行修正，使之能合理反映中主应力比对土体峰值内摩擦角的影响。修正后的准则在偏平面上的强度线与Lade-Duncan准则相似，但更具灵活性，预测结果更符合松砂真三轴试验结果。由于土体在加载过程中常发生应变局部化现象，导致其强度得不到充分发挥。基于非共轴塑性模型的分叉分析研究了应变局部化发生对土体强度发挥的影响，通过与密砂真三轴试验结果对比表明，分叉强度能合理反映在不同中主应力比条件下应变局部化发生对土体强度的降低作用。

Strength of soils considering the influence of deformation bifurcation under true triaxial condition

By using Lode angle, a shape function is proposed to describe the curve of strength criterion in octahedral plane, and then the Mohr-Coulomb criterion is revised to predict the influence of the intermediate principal stress ratio on the peak friction angle of soils correctly. The revised strength criterion is shown to be able to produce the same curve with Lade-Duncan’s criterion in octahedral plane, while it is suitable for predicting the strength of loose sands under true triaxial condition. In the loading process, the deformation of soil body often accompanies with strain localization, which makes the mobilized strength of soils to be reduced. The reducing effect on the strength of soils by strain localization is justified by bifurcation analysis. By comparing to the experimental results, it is shown that the mobilized strength of dense sands can be correctly predicted by the bifurcation analysis of non-coaxial plasticity under different intermediate principal stress ratio conditions.