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

两个世界知名的弹塑性本构模型，原始Cam Clay模型和修正Cam Clay模型，被扩展为适用于ko固结天然土壤沉积物的各向异性形式，并通过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概念，进一步扩展为适合描述重复加载下土壤行为的形式。从理论和数值的角度对这两个扩展模型的检验表明，它们在有限条件下可用于工程实践，并表明需要开发一套适用于更广泛种类的砂质土的本构模型。新开发的模型家族包括原始和修正凸轮粘土模型，并被发现适用于各种各样的自然土壤沉积物。从隧道现场采集的密实细砂块状试样，在非常高的围压下进行了一系列等体积三轴试验。将三轴试验获得的本构参数与在掘进现场进行的标准侵彻试验获得的爆破次数N进行仔细比较，目的是将爆破次数N与本构模型所需的参数相关联。Nishigaki等人（1974,1980）经验提出的吹风次数N和砂的不排水抗剪强度之间的关系的确认是目标之一。因此，开发了基于SPT吹计数N的砂层参数估计程序，并通过在砂层现场进行的深开挖工作的计算机模拟，研究了它在工程实践中的工作方式。本文采用土/水耦合有限元程序进行了计算机模拟，并与开挖砂土中板桩墙的弯矩和变形监测结果进行了比较，结果令人满意。研究结果表明，对于以喷吹次数N为唯一可用力学性能信息的砂层，可以主要根据喷吹次数N来估计其本构参数，并适用于工程实践。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