考虑应力路径和加载速率效应砂土的弹黏塑性本构模型

 利用室内多应力路径平面应变压缩试验结果，分析和研究密实砂土变形和强度特征的应力路径和加载速率效应。试验结果表明：一方面，不可恢复体积应变和剪切应变都具有明显的应力路径相关性，因而在传统塑性理论中将其作为硬化参量存在不合理性；另一方面，砂土的应力–应变特性与加载速率的变化存在着显著的关系。加载速率效应与蠕变和应力松弛一样均是砂土黏性的外在反映，其最重要的特征之一是加载速率发生突变时，应力也发生相应的突变，并呈现出刚性很大、近似弹性的特性。对试验结果的进一步分析发现，一种修正的不可恢复应变能W ir*及相关的函数与应力路径不相关。将W ir*作为硬化参量，并在非线性三要素模型的理论框架下，提出一种基于能量的砂土弹黏塑性本构模型。该模型可以考虑应力路径、压力水平、固有各向异性、孔隙比等因素对砂土变形和强度特征的影响，以及应变局部化和加载速率变化所产生的黏性特性。将上述模型嵌入到有限元程序中，并对平面应变压缩试验进行模拟计算，验证模型的精确性。研究结果表明，与现有的砂土本构模型相比，所提出的模型能更好地模拟应力路径及加载速率变化对砂土变形和强度特征的影响。

ELASTO-VISCOPLASTIC CONSTITUTIVE MODEL OF SANDY SOIL CONSIDERING STRESS PATH AND LOADING RATE

Based on the experimental results of drained plane strain compression(PSC) on saturated dense sandy soil along a wide variety of stress paths，the effects of stress path and loading rate on the deformation and strength characteristics of sandy soil are investigated. It is found that the irreversible shear strain and irreversible volumetric strain are dependent on stress history and stress path. And significant loading rate effect is observed in the tests. The same as creep deformation and stress relaxation，loading rate effect should be attributed to the viscous properties of the sandy soil specimens. One of the most important characteristics of loading rate effect is the stress changes sharply with a very high stiffness，nearly elastic behavior，when the strain rate suddenly changes. Subsequently，the use of any quantity shown above as the hardening parameter is not well reasonable in the traditional plastic theory. Based on the analysis of these test results，a novel modified irreversible strain energy，Wir*，and the related function are shown to be stress path-independent. An energy-based elasto-viscoplastic constitutive model of sandy soil，described in a nonlinear three-component framework，is proposed with the use of Wir* as the hardening parameter. The presented model can take into account the effects of stress path，pressure level，inherent anisotropy，void ratio，work softening associated with strain localization into a shear band and loading rate effect on the stress-stain behavior. The finite element method code incorporating the presented model is validated by simulating the PSC tests. It is shown that the proposed model can much better simulate the effects of stress path and loading rate on the deformation and strength characteristics of sandy soil than the previous models.