soil - self filtering criteria 1

[Corb04]

I am working on a paper about flow of water through soil. Someone told me that there is a "self filtering" criteria that is based on the grainsize distribution of the soil. Does anyone know of it and have a reference.

 

[BigH]

Check out Terzaghi Peck and Mesri (1995) - they have some good sections on soil filters - even if a soil is "self filtered". Also work by Cam Kenny of University of Toronto should be referenced. ASCE Journals of last 2 years had some papers on this. I believe that Vic Milligan's 34th Terzaghi lecture included some comments on filters for dams.

 

[Focht3]

Don't forget any of the books and papers written by Harry Cedergren. Clear, concise, readable, useful - worth their weight in gold...

And you can also look at the COE specs -



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[Corb04]

Thank you very much for your assistance. I will proceed in these dirctions.

 

[harney]

Self-filtration, also known as "bridging", is the formation of a "filter bridge" in the base soil immediately adjacent to the filter (whether it's a granular or geosynthetic filter). This refers to the ability of a base soil to retain its own finer particles near the base-filter interface. The mechanism involved is the migration of finer particles into the filter. The "layer" of base soil immediately adjacent to the filter becomes coarser, and subsequent layers moving away from the filter retain more and more of their fines. The system eventually comes to equilibrium, and no more fines are lost into the filter. The base soil is then "self-filtering". A base that is not self-filtering is incapable of forming a filter bridge (in a state of equilibrium) and more and more fines are piped from the base into the filter, possibly resulting is failure of the filter system (due to clogging or blinding) or settlement/deformation issues in the base soil unit (due to excessive soil loss and lack of retention). Note that the concept of "self-filtering", regardless of its name, does not imply that some sort of filter is not required.

Probably the best reference on this topic is Lafleur et al (1989) "Filtration of Broadly Graded Cohesionless Soils" ASCE JGE, 115(12) pp 1747-1768. For basic understanding of filters (or seepage in general), I concur with Focht3 that Cedergren can't be beat. If dealing with geosynth' filters, check Koerner's book or Holtz, Christopher and Berg (1997). For some great design guidance check out "Embankment Dams Granular Filters and Drains" ICOLD Bulletin 95.