饱和砂土的三剪弹塑性边界面模型研究(一)——模型理论

基于边界面模型方法研究了不同密实度和含泥量的饱和砂土在静、动荷载作用下的力学和变形特性。其中,初始边界面方程是通过改进修正剑桥模型椭圆形屈服方程得到的,后继边界面方程则是在前次边界面方程的基础上采用中心点映射法获得。针对原模型破坏应力比为定值,不能反映全应力状态和黏聚力在土体受力过程中的作用这一问题,基于三剪统一强度准则,通过等量代换法、坐标平移法对破坏应力比、相变应力比进行了修正,使修正后的椭圆形边界面适用于不同密实度和含泥量的饱和砂土。在此基础上应用边界面理论,研究了饱和砂土的三剪弹塑性边界面本构模型及有限元算式。该模型能够描述密实砂土在受力时表现的剪胀特性,同时可以反映中间主应力效应、应力区间效应、拉压差效应和黏聚力对应力-应变特性的影响。

Approaches to the triple-shear elasto-plasticity bounding surface model for saturated sands(1)-model theory

Based on the bounding surface model,the mechanical and deformation properties of saturated sands with different compactness and clayey content under static and dynamic loads are studied.Among them,the initial bounding surface equation isobtained through improving the modified Cambridge elliptic yield equation,and the subsequent bounding surface equations are developed based on the previous one with the rule of center point mapping method.The failure stress ratio of the original model is a fixed value,which does not reflect the role of the full stress state and cohesion in the process of soil stress.Based on the triple-shear unified strength theory,the failure stress ratio and the phase transformation stress ratio are modified by the equal-substitution method and the coordinate translation method.The modified elliptical bounding surface is suitable for saturated sands with different compactness and clayey content.On this basis,the triple-shear elasto-plastic boundary surface constitutive model and finite element formula of saturated sand are studied by using the bounding surface theory.The model can describe the dilatancy characteristics of compacted sand under stress,and can reflect the effects of the intermediate principal stress effect,the stress interval effect,the failure difference between tension and compression and cohesion on stress and strain characteristics.