Study on the Evaluation Method of the Engineering Properties of In-situ Sand Grounds

本文通过室内静剪和动剪试验以及原状砂的合作研究，得出以下结论：（1）变形-强度特性的微观检验1.粒状体的组构各向异性至少取决于接触法线的分布、颗粒的形状和相关空隙的形状。分别讨论了这些元素，给出了相应的二阶对称组构张量下的格布质各向异性定义.考虑循环荷载作用下组构变化的机理，估算了循环剪应力历史的影响。将这种剪应力历史效应的估计引入到基于“复合动员面”的应力-应变模型中，分析了沿八面体面旋转应力路径的各种循环真三轴试验。分析结果与实验值吻合较好。 ...更多信息 砂的强度对其强度特性有较大的影响，特别是在较高的密度和较低的围压条件下，其影响更为显著。(2)砂土地基原位强度评价1.通过原位冻结法获得的样品的质量被判断为相当好的基础上的事实，即砂样满足要求，以保持其结构在冻结过程中，和液化潜力的评估基础上的循环试验数据通过原位冻结法获得的样品似乎是一致的估计现场行为的砂土地基.对两种原状砂进行的一系列循环不排水三轴试验结果表明，天然原状砂沉积物具有明显的各向异性时程模式。这些各向异性的循环变形性能使得循环不排水三轴强度值差异显著.从天然存款中取样的相对干净的砂的各向异性循环变形-强度特性的特征可以通过合适的样品制备方法来再现，该样品制备方法可以模拟块体取样过程。(3)对循环不排水三轴试验方法的探讨根据合作循环不排水三轴试验的结果，提出了至少应规定试样制备方法、试样形状等试验条件，以减小试验数据的变异性。少

The following conclusions may be drawn based on the static and cyclic shear tests conducted in the laboratory as well as in the co-operative research of undisturbed sands;(1) Microscopic examination on the deformation-strength properties1. Fabric anisotropy of a granular mass depends at least on the dstribution of contact normals, the shape of particles and the shape of associated voids. These elements were individually discussed to give the corresponding definitions of gabric anisotropy in terms of second-rank symmetric fabric tensor.2. The effect of cyclic shear stress history was estimated considering the mechanism of fabric change under cyclic loading. Introducing this estimation of the effect of shear stress history to the stress-strain model based on the "compounded mobilized planes", various kinds of cyclic true triaxial tests along the rotational stress paths on the octahedral plane were analyzed. The analytical results agreed well with the experimental values.3 The initial fab … More ric of sand has a considerable influence on its strength properties, in particular a predominant influence is exerted in the conditions of a higher density and a lower confining stress.(2) Evaluation of in-situ strength of sand grounds1. The quality of the sample obtained by the in-situ freezing method was judged quite good based on the facts that the sand sample satisfied the requirements for preserving its structure during freezing, and that the evaluation of liquefaction potential based on the cyclic test data for the sample obtained by the in-situ freezing method appeared to be consistent with estimated field behavior of a sand ground.2. The reaults of a deries of cyclic undrained triaxial tests on two kinds of undisturbed sand indicated that natural in-situ sand deposits displayed a significantly anisotropic time history pattern. These anisotropic cyclic deformation performance make a remarkable difference in the cyclic undrained triaxial strength value.3. The feature of anisotropic cyclic deformation-strength properties of relatively clean sand sampled from natural deposit could be reproduced by a suitable sample preparation method which may simulate the block sampling procedure.(3) Examination of undrained cyclic triaxial test methods On the basis of the results of the co-operative undrained cyclic triaxial tests, it is shown that the test conditions such as sample preparation method and specimen shape should be specified at least to minimize the variation of test data. Less