真三轴条件下原状黄土的非线性本构模型

为了研究复杂应力条件下非饱和原状黄土的非线性本构模型，通过考虑真三轴条件下中主应力和吸力对大主应变的影响，提出了一个考虑中主应力影响的非饱和原状黄土的非线性本构模型。该模型包含12个参数，均可由常含水率非饱和土真三轴试验确定。研究了中主应力对土体变形和强度的影响，探讨了模型参数的变化规律。初始吸力一定时，土体的黏聚力随着中主应力的增大而增大，而内摩擦角随着中主应力的增大呈线性减小趋势。当吸力小于162 kPa时，吸力摩擦角等于21.8°；当吸力大于162 kPa时，吸力摩擦角等于5.5°。初始吸力相同时，不同中主应力条件下土体的体积模量可取为常数。利用该模型预估了常含水率真三轴等向固结试验的吸力变化规律，理论结果与试验结果比较接近。但是对于真三轴剪切试验吸力的预估还需要进行深入探讨。

Nonlinear constitutive model for intact loess in true tri-axial tests

To study the nonlinear constitutive model of unsaturated intact loess under the condition of complex stress, by considering the effects of the intermediate principal stress and suction on the major principal strain under the condition of true triaxial test, a nonlinear constitutive model considering the effects of the intermediate principal stress for unsaturated intact loess is developed. The model contains 12 parameters, which can be determined by the true triaxial tests of unsaturated soil with constant water content. The effect of the intermediate principal stress on the deformation and strength of soil is studied, and the change rules of the model parameters are discussed. When the initial suction is constant, the cohesion of the soil enlarges with the increase of the intermediate principal stress, while the internal friction angle decreases linearly with the increase of the intermediate principal stress. When the suction is less than 162 kPa, the suction friction angle is equal to 21.8°. If the suction is greater than 162 kPa, the suction friction angle is equal to 5.5°. When the initial suction is the same, the bulk modulus of the soil under the condition of different intermediate principal stresses can be taken as a constant. The model is used to predict the variation of suction in the true triaxial isotropic consolidation test with constant moisture content. The theoretical results are found close to the experimental results. However, the prediction of suction of true triaxial shear test still needs to be further explored.