Study On Permeating Characteristic Of Noncohesives Soil And The Mechanism Of Seepage-failure

Noncohesives soil is the general designation of all kinds of sand and grit, including pebbles. The grain size changes between a wide range and it is distributed abroad in nature with rich reserves. Noncohesives soil has many excellent engineering characteristic such as better compaction, fine water permeability, higher anti-press strength, etc. It was widely used during construction and operation of the project. The seepage failure must be considered under the condition of seepage action, no matter it was used for seepage material or dam foundation soil.Noncohesives soil's characteristics such as seepage and pipe seepage were deeply studied including indoor experiment and calculation by our forefathers, and a series of empirical formulas and theoretical formulas were educed. Based on forefathers' researches, the seepage characteristic and pipe seepage mechanism were deeply studied, and the following three aspects were completed:(1) Starting from soil texture, the factors that do affect to the permeability coefficient were analyzed. A new computation method was put forward though the help of experiment, in which, the noncohesives soil's grain size and the degree of compaction were well controlled. This new method and the former methods were taken to compare and contrast, and the result indicates that the results coming from this new method can well fit the experimental data and the results were reliable and accurate.(2) The hydraulic conditions of pipe seepage were studied. Considering both vertical seepage and horizontal seepage, the moving grain with different diameter was analyzed under the conditions of laminar flow and turbulent flow, and different critical hydraulic gradients were educed according to different pipe seepage.(3) The leaking passage mathematical model which was formed after pipe seepage failure was established. The well-flow theory coming from groundwater dynamics was brought in, and the sediment transport was taken into account, with the help of above, the pipe seepage mechanism was elaborated, the out flowing sediment and the stratum head and the distributing of permeability coefficient were calculated.