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Bearing capacity of cohesive soil with surface crust

带表层粘性土的承载力

基本信息

批准号：
61460163
负责人：
KIMURA Tsutomu
金额：
$ 3.01万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1986
资助国家：
日本
起止时间：
1986 至 1987
项目状态：
已结题

项目摘要

An attepmt was made to develop a new experimental technique with which a normally-consolidated clay layer overlain by hard syrface crust can be made. A series of centrifuge model tests was carried out using this technique and the bearing capacities were predicted by the upper-bound theory. Following conclusions were obtained from this study.1. The two-step consolidation has proven to be very successful for making normally-consolidated clay with surface crust; lst step --- To consolidate clay slurry layer by layer under the lap. floor reducing the consolidation pressures. 2nd step --- To turn upside down the consolidated clay and consolidate it in centrifugal field.2. The bearing capacitites are higher when the strength of the crust is higher and particularly large deformations take place in the area of the interface between the crust and nomally-consolidated clay where the strength is lowest.3. When the ratio of the strength at the crust surface(c_<u2>) to that at the interface(c_<u1>) is around 1/5, the bearing capacities become smaller with the increase of the width of footings. This trend is opposite to that observed for normally-consolidated clay layers without surface crust.4. Bearing capacities calculated by the upper-bound calculations are approximately 30% higher than the experiments, although failure mechanisms theoretically obtained agree fairly well with the observations. It has been found experimentally that the bearing capacity factor N_c increases with the strength ratio c_<u2>/c_<u1>l. The upper-bound calculations confirms this result.

本文试图发展一种新的实验技术，用这种技术可以制作上覆硬结皮的正常固结粘土层。利用该技术进行了一系列离心模型试验，并利用上限理论预测了承载力。本研究得出以下结论：1.两步固结法已被证明是非常成功的，使正常固结的粘土与表面地壳：第一步---粘土浆层一层一层地固结下一叠。降低固结压力。第二步-将固结好的粘土翻过来，在离心力场中固结.地壳强度越高，承载力越高，特别是在地壳与正常固结粘土的界面处，强度最低的地方，发生了特别大的变形.当壳面强度与界面强度之比<u2><u1>为1/5左右时，地基承载力随基础宽度的增大而减小;这一趋势与正常固结粘土层中没有结皮的情况相反。上限计算计算的承载能力比实验高出约30%，虽然理论上获得的失效机制与观测结果相当吻合。试验表明，承载力系数N_c随强度比c_<u2>/c_<u1>l的增大而增大。上限计算证实了这一结果。