Low permeability granular soil?

[Fynch]

Hello,

I have GI report which states the ground condition as made ground. And shows in most locations no cohesion. However, the permeability is quite low at 1x10-6 m/s.

So I'm confused - on the one hand it suggest a granular type material but on the other suggests there should be quite a bit of silt/clay.

Could it be that previously the made ground was compacted/settled to result in the low permeability value?

 

[GeoEnvGuy]

So the report is telling you its likely fill silty sand.

 

[fattdad]

10^-6 m/s=10^-4 cm/s. That'd be consistent with a silty sand, perhaps? It's not, "Low permeability," per se.

f-d

ípapß gordo ainÆt no madre flaca!

 

[cvg]

if there is zero cohesion, likely very little clay but up to 50% fine material is still classified as granular and percolation will be slow

 

[PEinc]

There is a big difference from "having no cohesion" to "recommending no cohesion."

http://www.PeirceEngineering.com

 

[geotechguy1]

Permeability can be significantly influenced by the gradation of the material and the fines content. For example, a well-graded sand-gravel with 10% fines could actually have a permeability even lower than what you reported. I believe even at ~15-20% fines permeability is dominated by the fines / fines matrix.

This is an area where the USCS classification system is really quite poor at giving a meaningful indication of soil properties or behaviour. The soil could be 20% silt-sized, 10% high plastic clay, and 70% sand and gravel, be classified as a cohesionless sand and gravel according to the USCS but have a very low permeability and behave in a 'clay like' manner.

 

[dik]

any frost heave possible... looks like a great soil for it...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Fynch]

Ah I see... would you say 3 x 10-7 is low permeability? I placed this clay layer as a boundary for seepage

 

[Fynch]

Also -if it's silty clay - how can there be no cohesion as the GI states?

 

[cvg]

you said it was granular with some silt or clay. that is not the same as saying it is silty clay. you have not provided much information to make an opinion

 

[BigH]

To throw out a thought, on a job in Toronto we used MTO Granular A - very well graded crushed graular sand and gravel with less than 8% fines. A foundation was going to sit on it for a paper machine (doing toilet paper if I remember correctly). The foundation was about 8 m below ground surface. After compaction, it rained. Water sat on it for 2 to 3 days. Mmmm

 

[dik]

Seen that lots of times with MTO Gran A...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik