正常固结非饱和黏性土的三剪弹塑性本构模型

TRIPLE-SHEAR ELASTO-PLASTIC CONSTITUTIVE MODELS OF UNSATURATED CLAYS IN NORMAL CONSOLIDATION

基于临界状态土力学框架,采用单应力变量法和双应力变量法非饱和土三剪强度准则,将原饱和土屈服函数中的屈服应力和破坏应力比分别替换成能反映土体饱和度影响的屈服应力和三剪破坏应力比,采用等量代换法和坐标平移法的三剪屈服函数推导出4种三剪弹塑性本构模型。所提本构模型能反映非饱和土全应力状态下土的强度区间效应、拉压强度差及黏聚力的影响。以南昌非饱和黏性土为研究对象,对所提4种模型分别做了试验参数确定、常规固结排水三轴试验验证和真三轴数值模拟分析。常规三轴试验结果表明,采用双应力变量相对单应力变量法的数值模拟结果相对更接近试验结果,采用坐标平移法相对等量代换法的数值模拟结果相对更接近试验结果。真三轴数值模拟对比结果表明,采用双应力变量法相对单应力变量法所得剪应力和体应变也偏大。随着中间主应力影响系数b增大,4种本构模型的剪应力和体应变也会随之增大;其他条件不变时,基质吸力越大,剪应力也随之变大。

In the framework of the critical state soil mechanics and adopting the triple-shear unified strength criteria with the methods of the single-stress variable and the double-stress variable for unsaturated soils,the yield stress and the failure stress ratio in the yield function of saturated soils are replaced respectively with the yield stress that can reflect the influence on soil saturation and the triple-shear failure stress ratio.Four triple-shear elastoplastic models of unsaturated clays are established with the methods of the equivalent substitution and the coordinate translation.These models can reflect the soil strength interval effects,the tension and compression strength differences and the cohesions for unsaturated soils under full stress states.The Nanchang unsaturated clays are taken as an example to determine the parameters of the four models,and to verify the models with the conventional triaxial consolidation drainage tests(CD tests)and true triaxial numerical simulations.The CD tests show that all the four models can well reflect the mechanical characteristics of the unsaturated clays.The models of the double-stress variable gave better approximations to the tests than that of the single-stress variable.The models with the equivalent substitution method fit better with the tests than that with the relative coordinate translation method.The true triaxial numerical simulation shows that the shear stresses and the bulk strains obtained by the double-stress variable method are larger than those obtained by the single-stress variable method.With the increase of the intermediate principal stress influence coefficient b,the shear stresses and the bulk strains from the four models will also increase.If other conditions remain unchanged,the shear stress increases with the increase of matrix suctions.