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

根据室内静力和循环剪切试验以及原状砂的合作研究，可以得出以下结论：(1)变形强度的微观检验颗粒体的结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。对这些元素分别进行了讨论，给出了织物各向异性的二阶对称张量定义。考虑循环载荷作用下织物变化的机理，估计了循环剪应力历史对织物的影响。将剪应力历史对基于“复合动员面”的应力-应变模型影响的估计引入到八面体平面上沿旋转应力路径进行的各种循环真三轴试验中。分析结果与实验值吻合较好砂的初始掺量对砂的强度性能有相当大的影响，特别是在较高密度和较低围应力的条件下，砂的强度性能受到较大的影响。(2)砂土地基原位强度评价2.原位冻结法获得的砂土样品满足冻结过程中结构的保存要求，液化潜力评价与原位冻结法获得的砂土地基的现场特性估计基本一致，表明原位冻结法获得的砂土样品质量较好。对两种原状砂土进行了不排水循环三轴试验，结果表明，天然原位砂土沉积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存在显著差异。采用合适的模拟块体取样的制样方法，可以再现天然沉积物中相对清洁砂的各向异性循环变形强度特性。(3)不排水循环三轴试验方法的检验根据协同不排水循环三轴试验结果表明，至少应规定试样制备方法和试样形状等试验条件，以尽量减少试验数据的变化。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