Constitutive models for sands under dynamic loading and constitutive parameters estimated based on SPT blow count N

利用Hashiguchi等人(1998)和Asaoka等人(2002)分别提出的扩展次加载面和超加载面的概念，将两个世界著名的弹塑性本构模型--原始的Cam Clay模型和修正的Cam Clay模型扩展为适用于Ko固结天然土体的各向异性形式，并进一步扩展为适用于描述重复荷载下土体特性的形式。从理论和数值的角度对这两个扩展模型进行了检验，结果表明它们在有限的条件下是可以在工程实践中使用的，并表明有必要建立一套适用于更广泛种类的砂土的本构模型。新开发的模型家族包括原始和修改的凸轮粘土模型，并被发现适用于各种自然土壤沉积。从隧道工地采集的致密细砂的原状块状样本接受…更多的是在很高的围压下进行一系列定容三轴试验。将三轴试验得到的本构参数与在掘进现场进行的标准贯入试验得到的击数N进行了仔细的比较，目的是将击数N与本构模型中所需的参数进行关联。验证Nishigaki等人(1974,1980)经验提出的砂土击数N与不排水抗剪强度之间的关系是目的之一。因此，开发了一种基于SPT的击数N的砂土参数估计方法，并通过对砂土场地进行的深挖工程的计算机模拟，检验了该方法在工程实践中的作用。结合新建立的本构模型，采用土/水耦合有限元程序对该模型进行了计算机模拟，并与开挖砂土中板桩墙体的弯矩和变形监测结果进行了比较，结果令人满意。得出的结论是，以SPT击数N为唯一力学性质信息的砂土的本构参数可以主要根据击数N来估算，并可应用于工程实践。较少

Two world-wide well known elastic-plastic constitutive models, the Original Cam Clay model and the Modified Cam Clay model, are extended into anisotropic forms applicable to Ko-consolidated natural soil deposits and further extended into forms appropriate to describe the soil behaviour under repeated loading by using the concepts both of extended sub-loading surface and super-loading surface proposed by Hashiguchi et al (1998) and Asaoka et al (2002) respectively. Examination of these two extended models from the theoretical and numerical points of view indicates that they are employable in engineering practice under limited conditions and suggests the need of developing a family of constitutive models applicable to wider variety of sandy soils. The newly developed family of models includes the Original and Modified Cam Clay models and is found to be applicable to wide variety of natural soil deposits.Undisturbed block samples of dense fine sand taken from a tunneling site are subjecte … More d to a series of constant volume triaxial tests under very high confining pressure. The constitutive parameters obtained from the triaxial tests are carefully compared with the blow count N obtained from the Standard Penetration Tests carried out at the tunneling site aiming at correlating the blow count N with the parameters needed in constitutive models. Confirmation of the relationship between the blow count N and undrained shear strength of sand empirically proposed by Nishigaki et al (1974, 1980) is one of the aims.A procedure of parameter estimation for sandy deposits based on the blow count N from the SPT is thus developed and examined how it works in the engineering practice by employing in a computer simulation of a deep excavation work carried out at a site of sandy deposit. The results obtained from this trial computer simulation using a soil/water coupled finite element code incorporating the newly developed constitutive model are found to be satisfactory by comparing with monitored bending moment and deformation of sheet pile wall installed in the sandy deposit being excavated. It is concluded that the constitutive parameters of sandy deposits for which the SPT blow count N is often the sole available information on mechanical properties can be estimated based primarily on the blow count N and applicable in engineering practice. Less