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Performance of Foundation for Uncemented Carbonate Sea Bed Sediments in the Southwest Islands

西南群岛非胶结碳酸盐海床沉积物地基性能

基本信息

批准号：
11660247
负责人：
SHINJO Toshiya
金额：
$ 2.18万
依托单位：
University of the Ryukyus
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
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/grant/KAKENHI-PROJECT-11660247/
关键词：
Calcareous sediments Geotechnical properties Ryukyu limestone Coral reefs Pile foundation Carbonate silt Carbonate sand Skin friction

项目摘要

Calcareous sediments such as coral reefs and Ryukyu Limestone are widely distributed in the Southwest Islands, Japan. These sediments include stronger cemented layer and softer uncemented material. This situation is problem for performance of foundation on such sediments from viewpoint of geotechnical engineering. Stronger cemented layers with sufficient thickness are used to be support layer for pile foundation on calcareous sediments expected loose uncemented sediments. In this study, the origin, structure of deposition and other factors involved in the foundation of these sediments are reviewed, and it is pointed out that it is necessary to clarify the mechanical properties of uncemented materials and understand the interface shear resistance on pile in order to employ a pile foundation on uncemented layers included in Ryukyu Limestone layer. A series of triaxial compression tests were carried out on carbonate silt, carbonate sand, Ryukyu Limestone crushed sand and lightly cemented carbonate sand. On the other hand, direct shear tests are performed on both carbonate sand and Ryukyu Limestone sand under the constant pressure test and the constant volume test. It is found that uncemented calcareous sediments exhabit large compressibility under compressive stress and also significant contractive volume strain when sheared. In such crushable sediments low shaft capacity of driven pile results from the decrease in the radial effective stress acting between the pile and the uncemented carbonate material due to contractive volume change. It is shown that skin friction for uncemented calcareous material to steel is evaluated from the test result of constant volume test. It is also suggested that grout is effective for the development of the shaft capacity of driven pile.

珊瑚礁、琉球石灰岩等钙质沉积物广泛分布于日本西南群岛。这些沉积物包括较坚固的胶结层和较软的未胶结物质。从岩土工程的角度来看，这种情况是地基在这类沉积物上的表现问题。对于疏松的未胶结的钙质沉积物，桩基支撑层采用强度较大、厚度足够的胶结层。本文综述了这些沉积物的来源、沉积结构及地基中涉及的其他因素，指出要在琉球石灰岩地层中的非胶结层上使用桩基，有必要弄清非胶结材料的力学性质，了解桩的界面抗剪强度。对碳酸盐粉砂、碳酸盐砂土、琉球石灰岩碎砂和轻质碳酸盐砂土进行了一系列的三轴压缩试验。另一方面，对碳酸盐砂土和琉球石灰岩砂土进行了定压试验和定容试验的直剪试验。研究发现，未胶结的钙质沉积物在压应力作用下耗尽了很大的压缩性，在剪切时也表现出明显的收缩体积应变。在这种可破碎的沉积物中，打入桩的低轴力是由于收缩体积变化导致桩与未胶结碳酸盐材料之间的径向有效应力减小所致。结果表明，非胶结石灰质材料与钢之间的表面摩擦力是由定容试验结果来评价的。灌浆对提高打入桩轴向承载能力是有效的。