正常固结饱和黏性土三剪有限变形弹塑性本构模型研究

基于三剪统一强度准则，利用等量代换法和坐标平移法分别推导出正常固结饱和黏性土的三剪破坏应力比，并将其与修正剑桥模型相结合，得到三剪统一屈服面方程。为反映饱和黏性土的变形非线性及大变形特性，基于有限变形理论，建立了正常固结饱和黏性土的三剪统一有限变形等量代换法和坐标平移法2种弹塑性本构模型。为验证模型的适用性，取江西红黏土制备三种不同压实度的试样，在不同围压下进行常规三轴固结不排水和固结排水压缩试验。将试验数据与本文所提2种有限变形模型及相应的2种小变形模型计算结果进行了对比分析，结果表明，随着变形的发展，有限变形模型相对于小变形模型更接近试验结果，能较好地反映黏性土因高孔隙率（低初始压实度、小围压及压缩变形前期）而产生的大变形特性，虽然小变形模型的计算偏差会随着土样初始压实度和所施加围压的增大而减小，但有限变形模型对不同压实度和围压的计算偏差均相对较小，其中，等量代换法有限变形模型在初始压实度较大或者围压较高时所得计算偏差相对最小。对所提本构模型所做真三轴分析表明，中间主应力影响系数b和初始压实度对土体的强度和变形特性具有一定的影响。主应力差、孔隙水压力和体应变与b值呈正相关性，主应力差与初始压实度呈正相关性，孔隙水压力和体应变与初始压实度呈负相关性。

Approaches to the Triple-shear Elasto-plastic Constitutive Models with Finite Deformations for Saturated Clays in Normal Consolidation

For soils in soft status, with high porosity or under high loading, the finite deformation theory should be used to analyze their deformation characteristics because the calculated results based on the small deformation theory may deviate from their actual practice which is not allowed. Based on the triple-shear unified failure criterion and the methods of equivalent substitution and coordinate translation, the triple-shear failure stress ratios for saturated clays in normal consolidation are derived and combine with the modified Cambridge model to obtain the triple-shear unified yield surface equations. Two triple-shear unified elasto-plastic constitutive models with finite deformations using the methods of equivalent substitution and coordinate translation are established to reflect nonlinear and large deformation characteristics for saturated clays in normal consolidation. In order to verify the applicability of these models, the conventional triaxial CU and CD tests are conducted for Jiangxi red clay samples with three compaction degrees under different confining pressures, and the experimental data are compared with the theoretical results obtained from the two finite deformational models and the corresponding two small deformational models. Conclusions show that the calculated results deduced from the constitutive models with finite deformational theory are closer to the test results compared with the models of infinitesimal deformational theory due to deformation development, so the former can better reflect the large deformation characteristics of the clays with high porosity caused by low initial compaction and low confining pressure in the early compression stage. Although the deformation deviations calculated with the infinitesimal deformation models would decrease with the increase of initial compaction degrees or confining pressures, deformation deviations with the finite deformation models are all relatively small with different initial compaction degrees or confining pressures. The finite deformation model with the equivalent substitution method gives the minimal deviations under conditions of large initial compaction degrees or high confining pressures. True triaxial simulations with the constitutive models proposed in this paper show that the influence coefficient b of the intermediate principal stresses and the initial compaction degrees have certain influences on the strength and deformation characteristics of the clays. Results show that the principal stress differences, the pore water pressures and the volume strains are positively correlated with b; the principal stress differences are positively correlated with the initial compaction degrees, while the pore water pressures and volume strains are negatively correlated with the initial compaction degrees.