考虑非饱和土基质吸力-回弹指数相关性的弹塑性本构模型及有限元实现

Swelling Index and Matric Suction Relations for Unsaturated Soil Elasto-plastic Constitutive Model in FEM

非饱和土压缩指数受基质吸力影响明显,回弹指数是土的临界状态本构模型中的重要变形参数。但在本构模型理论研究中,回弹指数随基质吸力的变化影响往往被忽略。为解决这一矛盾,以杭州地区重塑粉土为试样,使用GDS非饱和直剪系统的竖向加载功能,对试样进行50、100、200 kPa 3种定吸力条件下一维固结回弹试验,获取不同基质吸力非饱和回弹指数κ(s),并拟合得到κ(s)函数关系,对比已有试验研究,验证了拟合结果的合理性。进而将κ(s)表达式引入非饱和土扩展剑桥弹塑性本构模型,形成一种考虑回弹指数随基质吸力变化的非饱和土弹塑性本构模型。应用子增量步显示积分算法将该模型编辑成ABAQUS有限元UMAT子程序,最后基于ABAQUS有限元平台结合自编UMAT子程序进行固结回弹数值试验,模拟实际试验过程,对比两者试验结果,验证了该UMAT子程序的正确性。实现了一种考虑回弹指数随基质吸力变化的非饱和土弹塑性本构模型的数值化,为其进一步应用建立基础。

The swelling index,a crucial parameter for soil deformation,holds significant importance in the critical state elasto-plastic constitutive model.Unlike the compressibility index,which has been extensively reported in literature,the variation of the swelling index with matric suction has often been overlooked in theoretical studies of unsaturated soil constitutive models.To address this gap,oedometer tests were conducted on remolded silt specimens sourced from Hangzhou,China.Under suction-controlled conditions,utilizing an oedometer equipped with a GDS direct shear chamber,the experimental program comprised three tests conducted at matric suction levels of 50,100,and 200 kPa.The relationship between matric suction and the swelling index,denoted asκ(s),was established and fitted.Validation was performed by comparison with previous experimental studies.Furthermore,thisκ(s)relationship was incorporated into an unsaturated soil-extended Cam-clay elasto-plastic model.An explicit integration with a substepping error control algorithm was implemented within the ABAQUS finite element method(FEM)UMAT subroutine.The numerical modeling results of the silt oedometer tests,coupled with the UMAT subroutine,exhibited high agreement with laboratory tests.