循环荷载下砂土的剪切硬化边界面本构模型

A bounding surface constitutive model of sands with shear hardening

基于临界状态土力学框架,建立了一个适用于往返循环荷载作用的砂土边界面本构模型。采用无纯弹性域假设,认为受到反向荷载的瞬时土体就产生塑性变形,砂土的弹性区域退化为一个点。屈服面为倒子弹头型,由于砂土孔隙比与压力之间不存在惟一对应的关系,使得屈服面大小无法与体积应变直接耦合,故采用塑性偏应变而不是剑桥模型那种塑性体应变作为硬化参数。流动法则采用加入状态参数的修正的Rowe应力剪胀关系,体现了依赖状态的剪胀思想。屈服面大小的比值β反映了塑性模量的演化,并推导了dβ的表达式。只用1套参数,该模型就能合理地模拟砂土在不同密度和固结压力下循环荷载的应力-应变关系曲线。

Based on the framework of critical state soil mechanics, a new bounding surface constitutive model for sand, being applicable to cyclic loading, is proposed. No pure elastic region hypothesis is given in this model. Elastic region of sand reduces to a point. Reverse bullet-shaped yielding surface is adopted. No unique relationship between void ratio and the mean normal stress for sand prevents the direct coupling of yield surface size to void ratio. Incremental deviatoric strain is used as a hardening parameter, instead of adopted plastic volumetric strain as hardening parameter in Original Cam-clay model. The model combines the concept of state-dependent dilatancy by incorporating state parameter concept in Rowe＇s stress dilatancy equation. Bounding surface magnitude ratio β to loading surface gives plastic modulus evolvement. Formulation of dβ is deducted. A single set of model constants, once calibrated, can simulate cyclic stress-strain response under different initial void ratios and different confining pressures.