Effect of shear direction and shearing mechanism on undrained shear strength

各向异性固结天然粘土沉积物的不排水抗剪强度随剪切方向和/或剪切机制的不同而变化。从KO固结粘土地基中取出的样品被重新固结在剪切箱中，其中的样品被放置在与原位垂直方向倾斜的轴线上修剪的样品中。固结后，在与固结过程中施加的剪应力相比增大或减小的恒定体积条件下进行剪切，以模拟与竖直夹角平面上的地应力比，发现弹塑性本构模型与由此得到的不排水抗剪强度的实验各向异性相吻合，表明该本构模型有可能进一步应用于工程实践。通过对路堤固结地基的反分析，提出了本构参数的确定方法，并编制了有限元程序，使弹塑性本构模型不仅可以用来分析地基在荷载作用下的变形过程，还可以用来分析荷载作用下地基的极限破坏状态。对报告的失败案例记录的分析试验表明，所开发的方案在工程实践中取得了令人满意的效果。

Undrained shear strength of anisotropically consolidated natural clay deposits is mobilized to a different level of strength depending on the direction of shear and/or on the shearing mechanism. Samples taken from the Ko-consolidated clay subsoil are reconsolidated in a shear box in which samples trimmed with axes inclined to the in-situ vertical directin are placed. After consolidation, samples are sheared under constant volume condition with increasing or decreasing shear stress compared with the shear stress applied during consolidation aiming at simulating the in-situ stress ratio on the plane at angles with vertical.An elasto-plastic constitutive model is found to fit with thus obtained experimental anisotropy of undrained shear strength indicating that there may be further possibility of applying the constitutive model to engineering practice. A determination procedure of the constitutive parameters is then proposed together with the examination of the proposed procedure carried by performing the back-analysis of the subsoils under consolidation due to embankments.A finite element programme is developed in such a way that the elasto-plastic constitutive model can be employed in analising not only the deformation process of the subsoil under load but also the ultimate failure tate of the loaded subsoil. Trials of the analysis of reported case records of failure indicate that the developed programme works satisfactorily in engineering practics.