中文摘要：

针对上海粉细砂不存在唯一临界状态线的特点，对传统的砂土本构模型进行了改进，提出了一个能合理描述粉细砂剪胀性和应变软化特性的弹塑性本构模型。该模型采用双屈服面形式，可同时反映剪切变形及压缩变形机理。模型对传统修正剑桥模型中的剪胀性公式进行了改进，考虑了反映塑性体积应变由正转为负时对应的特征状态应力比与初始有效围压的相关性。为了描述应变软化特性，提出了一个利用残余状态应力比和峰值应力比的应变软化公式，可较为合理地反映粉细砂的应变软化特性。通过对上海粉细砂的多组试验结果模拟，验证了本文模型的合理性和有效性。

英文摘要：

On the basis of traditional model a modified elastoplastic constitutive model for fine sand which can reasonably describing the characteristics of dilantancy and strain softening is proposed. This two-yield surface model reflects the mechanism of shear deformation and mechanism of compressive deformation simultaneously. The traditional dilatancy equation of Cam-clay model is modified and the relativity between phase transformation stress ratio and initial effective pressure is considered. In order to describe the characteristic of strain softening, a strain softening equation using the stress ratio at steady state to peak state is formulated. The validity of this model is verified by several test results for fine sand in Shanghai.