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Development of the method for reducing the frictional restraint at the upper and lower ends of soil specimens by means of torsional ultra sonic wave excitation

扭转超声波激励减少土样上下端摩擦约束方法的研究

基本信息

批准号：
13650549
负责人：
TSUKAMOTO Yoshimichi
金额：
$ 2.3万
依托单位：
Tokyo University of Science
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

项目摘要

One of the most frequently used laboratory tests is a triaxial test, which assumes a cylindrical soil specimen bounded by upper and lower cylindrical plates, called "cap" and "pedestal", and soil specimens are subjected to compression. In order to acquire the deformation and strength characteristics of soils in an ideal manner, the soil specimens need to deform uniformly. However, they are subjected to the effects of frictional restraint from upper and lower ends. To make these effects as small as possible, the ratio of height to diameter of specimens is conventionally made 2. However, due to high costs of acquiring undisturbed soil samplesin the field, it is considered desirable to inccrease the number of soil samples by reducing the height of specimensThe first year of research was dedicated to examining if the ultra sonic wave excitation can be useful in reducing the frictional restraint of upper and lower ends of soil specimens for triaxial tests, which have been found to be useful … More in lessening friction in industrial applications. The generators for ultra sonic wave were housed in the cap and pedestal, and multiple series of triaxial compression tests were carried out, in which the height of specimens were varied. From the test results on Toyoura sand, it was found that the prevention of the development of frictional restraint was not achieved from the following reasons. (1) When the specimens are isotropically consolidated and are subjected to ultra sonic wave excitation, a large amount of volume contraction occurs, and formation of soil fabrics is disturbed. (2) When the specimens are axially loaded and are subjected to ultra sonic wave excitation, rapid reductions in shear stress occur again and again, probably due to volume contraction, which is induced rapidly in manner similar to above. From the test results on Fujinomori clay, the same curious phenomena as those of Toyoura sand were not observed. However, the frictional restraint was not completely removedThe last year of research was dedicated to examining the influence of ultra sonic wave excitation on the volume contraction of granular materials during consolidation and axial compression. The volume contraction during consolidation is found to become up to a few percent of volumetric strain, although the amplitude of ultra sonic wave is as small as 1 to 4 μm. When the ultra sonic wave excitation is applied to the soil specimens, which developed negative pore pressures, the reduction in shear stress occurs, which in turn causes the reduction in negative pore pressures, and even causes the development of positive pore pressures. Therefore, the volume contraction occurs upon drainage of pore water after the application of ultra sonic wave excitation Less

最常用的实验室试验之一是三轴试验，该试验假定一个由上、下圆柱板(称为“盖板”和“底座”)包围的圆柱土样，土样受到压缩。为了获得理想的土体变形和强度特性，土样需要均匀变形。然而，它们受到来自上端和下端的摩擦约束的影响。为了使这些影响尽可能小，通常使试件的高度与直径之比为2。然而，由于在野外获取原状土样的高成本，通过降低试件的高度来增加土样的数量被认为是可取的。第一年的研究致力于研究超声波激励是否有助于减少三轴试验中土样的上端和下端的摩擦约束，这已被发现是有用的…更多的是在工业应用中减少摩擦。将超声波发生器安装在试件的顶盖和底座中，进行了不同试件高度的多组三轴压缩试验。从Toyoua砂上的试验结果发现，由于以下原因，没有达到防止摩擦约束发展的目的。(1)当试件处于各向同性固结状态时，在超声波作用下，会发生大量的体积收缩，破坏土体组构的形成。(2)当试件承受轴向载荷和超声波激励时，剪应力反复快速降低，这可能是由于体积收缩引起的，这可能是以类似于上述方式快速诱导的。从藤森粘土上的测试结果来看，没有观察到与Toyoua砂相同的奇怪现象。然而，摩擦约束并没有完全消除。过去一年的研究致力于研究超声波激励对颗粒材料在固结和轴向压缩过程中体积收缩的影响。尽管超声波的振幅只有1~4μm，但固结过程中的体积收缩只占体积应变的几个百分点。当超声波作用于产生负孔压的土样时，剪应力会降低，进而导致负孔压的减小，甚至产生正孔压。因此，在施加超声波激励后，孔隙水排出时发生的体积收缩较少