Stability of a levee modelled in a geotechnical drum centrifuge.

日本第一台鼓式离心机的设计和制造是为了研究长土结构的稳定性问题，如堤防、堤防。鼓的直径为0.8米，宽度为0.3米，深度为0.1米，可旋转至150克，产生377米长，45米宽，15米深的土壤模型的原型行为。本研究的成果可以概括为以下几点：1。到1987年2月底，转鼓式离心机的安全运行已经持续了一千多个小时，这使我们有信心利用转鼓式离心机作为模拟岩土工程问题的有用实验工具。建立了在鼓内压实土堤防上覆正常固结粘土层的试验技术。成功地发展了洪水期间堤防破坏的建模技术。进行了不同土壤类型的模型试验。仔细观察表明，堤防的破坏过程可以用浅埋隧道稳定性的类比来理解。观察到的破坏过程如下：随着水位的升高，首先在堤防坡面发生侵蚀，水力破裂形成管流，渗水到达内陆侧堤防坡面。由于冲刷出土壤颗粒，管流直径逐渐变宽。我们对浅埋隧道稳定性的知识告诉我们，管道的稳定性由管道的覆盖与管道直径的比值，以及土壤的黏聚力和单位重量决定。对于粘性较高的土体，管材在管径较大时保持稳定，而粘性较低的土体，管材在管径达到一定值时发生坍塌，导致堤防完全破坏。

The first drum centrifuge in Japan was designed and constructed to study the stability problems of long soil structures, such as embankments, levees. The drum has the diameter of 0.8 m , the width of 0.3 m and the depth of 0.1 m , and can be spinned up to 150 g, producing the prototype behaviour of a soil model of 377 m long, 45 m wide and 15 m deep. The achievement of this study can be summarized in the following points.1. Safety operation of the drum centrifuge has continued for over one thousand hours by the end of Feburary,1987, which gives us a confidence of utilizing a drum centrifuge as an useful experimental tool for modeling geotechnical problems.2. Experimental technique of production of a normally consolidated clay layer overlain by a levee of compacted soils in the drum has been established.3. Modeling technique of levee failures during flood has been sucessfully developed. A series of model tests with different soil type was carried out. Close observation suggests that the process of failure of a levee may be understood by using an analogy of stability of shallow tunnels. Observed process of failure was as follows:As the level of water raises, the first erosion is occurred at the surface of a levee slope, and that a pipe flow is created by hydraulic fracture and seeping water reaches at the surface of the levee slope on the inland side. As the result of flushing out the soil particles, the diameter of the pipe flow gradually widens. Our knowlegde of the stability of of a shallow tunnel tells us that the stability of the pipe is gorverned by the ratio of the cover of the pipe to the diameter of the pipe, and by the cohesion and the unit weight of the soil. For soils having higher cohesion, the pipe remains stable up to relatively larger diamter, whereas soils having less cohesion, the pipe collapes when the diamter becomes a certain value, resulting the total failure of the levee.