Ali azad - M Sc. Student of Geotechnical Engineering
S.Shahab Yasrobi - Associate prof. of Civil Engineering

Granular Filter is one of the main parts in an embankment dam which can prevent soil erosion. Although filter has a simple mechanism to control erosion and seal the core crack, and also there are some criteria for designing , the excess of effective factors influencing the soil-filter behavior have made it complex for engineers to design a proper filter. Gradation curve, relative density of filter , soil compaction , grain shape, hydraulic gradient, physico, chemical properties, fine content, filter thickness, internal stability , problematic soils, etc. are the examples of these factors. Besides, this complex set can be easily simulated in laboratory to cover all of the effective whereas the other analysis or numerical models are not able to do so. NEF (no erosion filter) test is the latest which is frequently used. This paper describes the designing based on criteria in comprison with come laboratory results and shows how a direct test can design better than indirect rules

Gramular filter, Embankment Dams, NEF, Criteria