Spillway filter design

[TAC]

I am working on the redesign of a spillway for a small embankment dam. The existing spillway leaked causing errosion of the underlying silty clay soils. I am currently designing a filter for below the new concrete spillway. Does anyone have any suggestions based on experience or any good references? Any comments would be appreciated.

 

Excerpted from:<br>
DEPARTMENT OF THE ARMY U.S. ARMY CORPS OF ENGINEERS<br>
CEGS-02620 (August 1997)<br>
<br>
<br>
In order to minimize the migration of fines into the coarser material while maintaining adequate permeability, the following criteria should be met:<br>
<br>
All soils (except clays without a sand or silt fraction):<br>
<br>
(15 percent size of drainage or filter material)/(85 percent size of material to be drained) = 5 (max)<br>
<br>
(50 percent size of drainage or filter material)/(50 percent size of material to be drained) = 25 (max)<br>
<br>
(15 percent size of drainage or filter material)/(85 percent size of material to be drained) = 5 (max)<br>
<br>
(15 percent size of drainage or filter material = 0.4 (max)<br>
<br>
All Soils<br>
<br>
(15 percent size of drainage or filter material)/(15 percent size of material to be drained) = 5 (min)<br>
<br>
for slotted/perforated subdrain pipes:<br>
(50 percent size of drainage or filter material)/(slot width) = 1.2 (min)<br>
<br>
(50 percent size of drainage or filter material)/(hole diameter) = 1.0 (min)<br>
<br>
Additional information can be found in USACOE TM 5-820-2.<br>

 

[TAC]

Thank you

 

[nitpik]

you might consider installing a barrier to seepage...possibly a membrane cutoff placed by a trencher being careful to assure a water tight seal at the interface of the underside of the spillway structure with the cutoff membrane.