Spillway filter design 4

[TAC]

I am working on the redesign of a spillway for a small embankment dam. The existing spillway leaked causing errosion of the underlying soils. The underlying soil is a silty clay. 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.

 

[georam]

Filter design papers :<br>
1. Sherard, Dunnigan, Talbot, &quot;Filters for Silts and Clays&quot;, Journal of Geotech Engineering, ASCE, vol 110, n0. 6, June 1984<br>
2. Sherard, Dunnigan, Talbot, &quot;Basic Properties of Sand and Gravel Filters&quot;, J. of geotech Engrg, ASCE, vol 110, No. 6, June 1984

 

[georam]

More papers related to filter design :<br>
1. ICOLD Bulletin 95, 1994 &quot;Embankment Dams : Granular filters and drains&quot;<br>
2. u. Schuler, and J,. Brauns, &quot;The safety of geotechnical filters&quot;, Hydropower and Dams magazine, issue 6, 1997<br>
3 Book : Balkema Publication, 1993 : &quot; Filters in Geotechnical and Hydraulic Engineering :<br>
a. &quot;R. Holtz and G. Fischer , &quot; Geotextiles as Filters&quot;<br>
b. J. Lafleur, J. Mlynarek, A. Rollin, &quot;Filter criteria for well graded cohesion soils&quot;<br>
c. Y. Myogahara, S. Morita, H. Kuroki, &quot;Piping stability in the filter material of roackfill dams&quot;<br>
d. Ch. Baterau, &quot;Comparison of existing granular filter criteria<br>
<br>
<A HREF="mailto:halim@pangea.ca">halim@pangea.ca</A>

 

[TAC]

Thank you. The information is veryhelpful!

 

[dirtman]

The NRCS criteria for filter design together with step by step examples is given at the following URL:

http://www.ftw.nrcs.usda.gov/neh26.html

 

[TAC]

Thank you. That is a good refernece.I'm keeping that for future use.

New question:

The spillway has already been constructed. We used a graded sand and gravel filter. We were not permitted to use a geotextile as a filter. The Ohio Department of Natural Resources prohibited it. Their fear is clogging of the fabric with time and thus restricting the drainage to the outlet pipes. Has anyone had experience (pro or con) using geotextiles in a drainage system for important projects? I have a friend who is a geotechnical engineer for the Bureau of Reclamation and he says that they have used geotextiles in dams before in similar applications. So I began wondering if the resistance of the ODNR to letting us use geotextiles was based on previous poor performance of the materials in this types of application or for some other reason. Either way, we were running short on time and didn't debate the issue with them. Now I am just interested for my own information. I would appreciate any insight on this topic.

 

[dirtman]

I am in complete agreement with the Ohio agency. There is absolutely no justification to allow the use of geotextiles in a critical application where there is limited access to the installation for potential repair work. Granular filters in this situation would only be marginally more expensive and any experienced designer would have more confidence in the long term capability of the granular media to convey seepage flow.