Test Study On Piping By Sand-bank Model And The Mechanism Of Levee Piping

Foundation piping has great harmfullness and high frequency of occurrence, there is complexity and randomness in it’s development process. There is considerable controversy on the piping of levee seepage deformation mechanism at present. Therefore, the study of foundation piping has a very important practical significance.In this paper, it used the sand slot model tests to study piping phenomena in a variety of experimental conditions, and recorded the experimental phenomena and data, analysising and investigation the mechanism of the development of the piping destruction. On the Comparative analysis of the phenomenon and data of test, we can summary some rules of the development of the piping destruction, expounding foundation piping by the way of force analysis and reasonablely explain some phenomenons in the development of piping, which will be beneficial for improve the understanding of the mechanism of piping. The main achievements are in the following aspects:1. For ingle-deck chung orifice of foundation tube produce in the inside slope feet of the levee, the location of piping passageway occur in the top of the sand layer embankment foundation. The seepage failure of the single-deck foundation piping passageway, which uses flowing soil for the foundation, begin with the inside slope feet of the levee, while the seepage failure of the single-deck foundation piping passageway, which uses "piping" type soil for the foundation, begin with the top of the sand layer embankment foundation.2. For double-deck chung orifice of foundation tube produce in the weak place of covering layer, the location of piping passageway occur in the top of the sand layer embankment foundation. Whether the double-deck embankment found at uses flowing soil for the foundation, or uses "piping" type soil for the foundation, the seepage failure of the single-deck foundation piping passageway begin with the weak place of covering layer.3. The critical hydraulic gradient depends mainly on the character of the subject particles in the soil at the beginning of the seepage failure of the single-deck foundation piping passageway, which uses flowing soil for the foundation. While the critical hydraulic gradient depends mainly on the character the fine particles in the soil at the beginning of the seepage failure of the single-deck foundation piping passageway, which uses "piping" soil for the foundation, but the effect of coarse particle should not be neglected.4. For the double-deck foundation piping passageway, the critical hydraulic gradient at the beginning of the seepage failure and while connecting with upstream depends mainly on the covering layer and the levee body, rather than the character of the soil particles themslves. The critical hydraulic gradient at the beginning of the seepage failure depend on the thickness of the weak place of covering layer, at the same time, the critical hydraulic gradient at the process of piping passageway developing and while connecting with upstream depend on foundation stress created by the levee body.