Permeability of Sand-Clay Mixtures

[bdbd]

Hello everyone,

I had a really important problem and performed an extensive literature search, however, I couldn't find anything except few articles.

My problem is: Sand's permeability.

We all -I think- sand settles almost immediately due to high permeability. Howewever, in a project, I had a chance to get UD from clayey sands and oedometer test yields very low permeabilities although sand ratio is around 75% and clay is around 15-20%.

When I looked it up, I found an article that performed consolidation tests on different sand-clay ratios. I saw that even 10% clay ratio is decreasing permeability to 10-8 m/s.

What experience do you have on this issue? Do you have any resource? I really don't want to say there is a time-dependent settlement in sands, however, it seems like that. I would like to discuss this issue and waiting any contribution from you guys.

Thanks.

 

[fattdad]

there are correlations based on D10 and D20. It does't take much reduction in D20 or D10 to change the permeability.

f-d

ípapß gordo ainÆt no madre flaca!

 

[oldestguy]

Your experience:
"very low permeabilities although sand ratio is around 75% and clay is around 15-20%."
is very common and to be expected.

In my experience, landfill cover construction, it doesn't take much clay to really lower the permeability of the mix. However, get your clay content much higher and you run into the problem of shrinkage and the resu8lting cracks make for significant infiltration potential.

Here was a funny experience. Years ago the early on Wisconsin DNR management engineers were going to show me (a consulting engineer) one of their pride landfills where they required a high clay percentage in the cover. It was a 1.5 hour trip each way. The landfill had been closed for three years. It was summer time. As we walked out on the landfill, in the tall grass I noticed cracks in the cover and shoved a folding rule down about three feet into the solid waste via these many open cracks. On the way to the site they "preached" to me as to what it takes to "do a good job". Needless to say, on the way home, they were totally silent. However, they turned out to be great friends and referred landfill prospects to me for advice.

 

[PEinc]

I remember from soil mechanics class many moons ago the professor mentioning that as little as 15% clay content can choke off the sand's permeability.

http://www.PeirceEngineering.com

 

[geomane]

The Northwest Florida ERP Manual has a graph showing hydraulic conductivity vs fines content. I think UF students may have developed the graph based on hundreds of permeability tests run on Florida sands with varying fines contents. May be worth a look.

 

[bdbd]

fatdad,

Yes, for example Hazen formula considers D10 and yields for 0.0013mm=D10, approximately 1.7 x 10-8 m/sec yields. Very low..

oldestguy,

I didn't know, thank you for these cases.

PEinc,

Your professor is definetely right. Nice term: choking.

jmcc3265,

Great resource! I found the document you told which is "REFERENCES AND DESIGN AIDS FOR ENVIRONMENTAL RESOURCE PERMIT APPLICANT’S HANDBOOK VOLUME II", Figure 1-12 shows the graph you mentioned.
Thank you very much. Is it published in a paper?

 

[Ron]

In my experience with SP and SP-SC materials, at about 10 to 15 percent clay content, the unit weight jumps up significantly in laboratory compaction and the permeability drops by one to two orders of magnitude...from 10^-3 to 10^-5 cm/s. Keep in mind that clay particles are significantly smaller than sand particles and will easily fill those interstitial voids in sand.

 

[fattdad]

permeability can also vary by two or three orders of magnitude depending on the compaction moisture content. Refer to Mitchel, Hooper and Campenella (sp) where they show permeability of one soil all compacted to the same relative compaction, but showing variation by 3 orders of magnitude depending on whether the compaction was below the line of optimums or above. Much lower permeability when wet of the line of optimums!

Hazen is one of the correlations, but there are others.

f-d


ípapß gordo ainÆt no madre flaca!