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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，需要进一步对原状样品进行研究。然而，通过扰动样品的管道试验可以得出以下结论：土壤颗粒可以在骨架结构的间隙内迁移，并且如果受到足够的水力梯度，可以从斜坡表面被冲走。这是渗流破坏的第一阶段。不损失颗粒的土称为具有稳定级配，而容易损失颗粒的土则为不稳定级配。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土为稳定状态，对应于均匀性系数Uc≥20和稳定性指数H/F≤1.3，这些当D≥2.4时，由于D是由粒度分布曲线的形状导出的，因此容易不稳定。根据这个新的限制，Shirasu的三分之五是不稳定状态。在这种情况下，细粉的强烈管道发生在几乎是经典管道理论给出的临界梯度的二分之一到三分之二的梯度处。因此，悬崖处的破坏过程可以概括如下：细粉被冲走，并通过管道形成小渗孔。此后，孔扩大，孔底部被侵蚀，像孔周围的云母一样呈薄片脱落。然后它上面的部分由于自重突然滑落。