Investigation of Crushed Rock Filters for Dam Embankment

A laboratory investigation of crushed rock filters is made to evaluate the filter criteria needed for the sandy clays and silts of tropical residual soils. The ability of a downstream filter to seal a concentrated leak through a dam core is assessed. Behavior of the broad, graded, sandy, impervious soils are dominated by the fines fraction. The filter criteria is well represented by $D_{15}$ of filters and $d_{85}^{*}$ of base soils. The derived criteria, $D_{15}/d_{85}^{*}⩽12$ is conservative for judging the acceptability of crushed rock filters as protective filters. The filtering ability of graded filters is sensitive to the grading below the 15% size. The effects of remolding and saturation on the soil properties deserve consideration in the design of filters for the tropical residual soils. The Atterberg Limits of the soils have no significant influence on the needed protective filter.