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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.

目前的研究一直试图验证液化砂具有速率依赖性质，以及直接测量粘度系数。这一目标具有重要意义，因为液化引起的沙地变形预测是生命线设施以及河流堤防和港口结构安全的迫切需要。为此，许多研究机构进行了模型试验，并得到了几个粘度值。这种研究方法的缺点是模型试验不能直接测量液化砂的应力和应变，并且不能对由试验结果反算得到的黏度值进行检验。有了这个观点，本研究开始了实验室剪切试验来测量粘度。第一阶段采用空心圆柱扭剪装置，但收效甚微。从中得到的教训是；-液化试样在其顶部形成水膜，因此扭转剪切变得困难。-此外，由于在不排水条件下增加有效应力并使砂土变硬的膨胀，无法达到真正的液化状态。因此，第二阶段的研究采用了三轴压缩试验，其中在试样顶部可能存在的水膜不影响压缩力的加载。此外，在人为控制孔隙压力高、有效应力低的情况下，决定以排水方式进行试验。该研究的主要发现是；—液化砂的粘度系数为500 ~ 4000kpa。-干燥试样的粘度较小，表明水饱和试样中约50%的粘度是由孔隙水产生的；可能运动沙粒孔隙水中的涡旋起了重要作用。细粒冲积砂的粘度小于均匀级配砂。