Explanation of Seepage Failure Mechanism at Steep Slope of Shirasu Soil

Shirasu土陡坡渗流破坏机理解释

基本信息

批准号：
11460114
负责人：
MIWA Koichi
金额：
$ 4.61万
依托单位：
Kagoshima University
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

项目摘要

To clarily the mechanism of seepage failure at the steep slope of Shrasu (pyroclastic flow deposit), further works are required to study on undisturbed samples. However, the following conclusion can be drawn from piping tests of disturbed samples.Soil particles can migrate within the interstics of a skelton structure, and can be washed out from the surface of slope if subjected to a sufficient hydraulic gradient. This is the first stage of seepage failure. A soil will be described as having stable gradation if it does not lose the particles, whereas it has an unstable gradation if particles can casily be lost.To determine whether Shirasu soil was on internal stability or not, the useful limit was proposed in this research that Shirasu soil having a fractal dimension D≦2.4 was a stable state coresponding to unifomity coefficient Uc≧20 and stability index H/F≦1.3 and these having D≧2.4 was liable to be unstable, where D was derived from the shape of the grain-size distribution curve. According to this new limit, third fifth of Shirasu were unstable states. In this condition, the strong piping of fines took place at gradients of almost one half to two third of the critical gradient given by the clasical piping theory.Therefore the process of failure at the cliff can be smmurized as follows ; the fines are washed out and the small seepage hole is formed by piping. After that, the hole is enlarged with the erosion at the bottom of the holes as coming off in thin section like mica around the hole. And then the part above it slides suddenly down by its own weight.

为了明确Shrsu陡坡（火山碎屑流沉积物）渗流破坏的机制，还需要对未扰动样品进行进一步的研究。但是，从受扰动样品的管道测试中可以得出以下结论。土壤颗粒可以在其内部迁移。如果有足够的水力梯度，则可以将土体从斜坡表面冲走，如果没有，则称土体具有稳定的级配。为了判断 Shirasu 土是否处于内部稳定状态，本研究提出了有用的极限：分形维数 D≤2.4 的 Shirasu 土为稳定土。对应于均匀性系数Uc≥20和稳定性指数H/F≤1.3的状态，且D≥2.4的状态容易不稳定，其中D由形状导出根据这个新的限制，Shirasu 的三分之二是不稳定状态，在这种情况下，细粉的强烈管道化发生在几乎是经典管道化理论给出的临界梯度的二分之一到三分之二的梯度上。因此，悬崖处的破坏过程可以概括为：细粉被冲走，并通过管道形成小渗孔，然后随着孔底的侵蚀而脱落，孔扩大。孔周围像云母一样薄的部分，然后它上面的部分由于自身重量突然滑落。