Document Type : Article
Authors
1
School of Agricultural Shiraz University
2
Dept. of Civil Engineering\r\nIslamic Azad Universi&z
Abstract
Investigations have shown that the main reason for embankment dam failure is piping through the embankment or foundation. The Balder Head dam in England, the Teton and Baldwin Hills dams in the US, and the Nanak Sagar dam in India are some dams which have failed due to a filter disability in stopping washed materials. The central core of embankments and gravel dams consists of deposits that have significant amounts of fine content. Therefore, filters in the embankment dams are designed to retain eroded fine particles from this kind of soil, to make the core and whole dam structure safe. In other words, the filter layer must be so fine that it is able to stop the erosion of protected soil and be so coarse that it has a sufficient discharge capacity to prevent excessive pore pressure. In successful filters, only in the first moment of flow, particles of base material completely pass through the filter layer and are washed. Subsequently, coarser particles of the base material clog pores of the filter and these particles hold the finer particles, so, a stable condition is formed on the whole common surface of the filter and core. In fact, the most important unanswered question regarding filter performance concerns the ability to resist crack formation, and prevent leaks through adjacent cracked or distressed zones. To address these concerns, a new test apparatus has been developed to evaluate filter performance, when both the filter and the core are cracked. In the case of successful filters, they slump to fill the crack, flow rate decreases, and head water pressure increases to earlier pressure. In the failed filters case, the flow rate does not decrease and remains high, also a very low head water pressure take place. In this research, variations of pressure, fines content of filter soils, compaction time and amount of eroded materials were evaluated. Results showed that the prime flow rate increased as the hydraulic gradient increased, but decreased in a little time and reached a stable value. A filter with 15% non-plastic fine content, had the ability to slump to fill the crack, but its coefficient of permeability decreased significantly, and, hence, cannot be used as a filter in embankment dams.
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