Laboratory shear tests on rate-dependent nature of liquefied sand undergoing large deformation

大变形液化砂速率依赖性的实验室剪切试验

基本信息

批准号：
11450179
负责人：
TOWHATA Ikuo
金额：
$ 8.58万
依托单位：
University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B).
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-11450179/
关键词：
sand torsion shear tests undrained tests large deformation viscosity liquefaction

项目摘要

The present study has been attempting to verify that liquefied sand has a rate-dependent nature, as well as directly measuring the viscosity coefficient. This aim has been important because prediction of liquefaction-induced deformation of sandy ground is urgently needed for safety of lifeline facilities as well as river dikes and harbor structures. Model tests have been conducted by many research institutes for this goal and several values of viscosity have been obtained. The shortcoming of this way of study is that model tests cannot directly measure the stress and strain of liquefied sand, and the values of viscosity as back calculated from test results cannot be examined.With this view point, the present study initiated laboratory shear tests for measuring the viscosity. In the first stage, a hollow cylindrical torsion shear device was employed with little success. The lesson learned from it are ;- A liquefied specimen forms a water film at its top and consequently torsion shear becomes difficult.- Moreover, the true state of liquefaction cannot be attained because of dilatancy which under undrained conditions increases the effective stress and makes sand stiff. Accordingly, the second stage of study employed triaxial compression tests in which a possible water film at the specimen ユs top did not affect loading of compressional force. Moreover, it was decided to run tests in a drained manner while controlling artificially the pore pressure high and effective stress low.The major findings from the study are ;- The viscosity coefficient of liquefied sand is in the range of 500 to 4000 kPa.- A dry specimen exhibits a smaller viscosity, suggesting that about 50% of viscosity in a water saturated specimen is generated by pore water ;probably vortex in pore water among moving sand grains plays an important role.Alluvial sand with fines has a smaller viscosity than uniformly graded sand.

本研究一直试图验证液化沙具有速率依赖性，并直接测量粘度系数，这一目标非常重要，因为为了生命线设施的安全，迫切需要预测液化引起的沙地变形。以及河堤和港口结构，许多研究机构为此进行了模型试验，并获得了多个粘度值。这种研究方式的缺点是模型试验不能直接测量应力和应力。液化砂的应变，并且无法检查根据测试结果计算出的粘度值。鉴于此，本研究启动了用于测量粘度的实验室剪切试验。在第一阶段，采用了空心圆柱扭剪装置。从中吸取的教训是：-液化样本在其顶部形成水膜，因此扭转剪切变得困难。-此外，无法获得液化的真实状态，因为因此，研究的第二阶段采用了三轴压缩试验，其中样本顶部可能存在的水膜不会影响压缩力的加载。以排水方式进行测试，同时人为控制高孔隙压力和低有效应力。研究的主要发现是；-液化砂的粘度系数在 500 至 4000 范围内kPa.-干燥的样品表现出较小的粘度，这表明水饱和样品中约 50% 的粘度是由孔隙水产生的；可能移动砂粒之间孔隙水的涡流起着重要作用。含有细粉的冲积砂具有较小的粘度。粘度高于均匀级配砂。