Percent Swell to Field Uplift Pressure

[mudcatwilly]

Let's say you have a soil sample taken from a 10-foot thick clay layer and the lab results give a 4% swell on the sample. How do you predict the soil uplift pressure in the field if all you are given is the percent swell of the sample?

 

[Jalthi]

I think you cannot, at least I cannot. Consider runnig pressure swell (or swell potential) test to determine the pressure required to limit the swell to a certain percentage.

 

[mudcatwilly]

Thanks for the reply. I have asked this question to at least 5 of my geotech colleagues and they have all said the same thing: "There is no direct correlation." The closest that I have to a correlation is a table relating probable expansion (% volume change) to a range of swelling pressures. For example: for a range of swell from 1% to 5%, you get a swell pressure of 3 to 5 ksf. The correlation is so loose that it's almost a guess.

 

[fattdad]

You can use the odometer to evaluate swell under varying confining pressures.

f-d

¡papá gordo ain’t no madre flaca!

 

[irawanfirmansyah]

More detail, run Swelling test ASTM D4546 Method B, to get both swelling magnitude and swelling pressure (see attached figure).

 

[ishvaaag]

Attached go 3 formulations related to swell pressure under foundations in a study made for the sole case at which I had to deal with soils with some potential of swelling (been known); they show to be quite consistent.

Essentially the insurance people was asking a change from generalized mat under attached homes to deeper fotings exerting more pressure. Through the study we were able to prove them that the technically foreseable pressure from swell was about a fourth the actual pressure under the foundation mat anywhere and no change was required to our (in our view) superior foundation, what they accepted.

 

[FixedEarth]

These soil tests intended for evaluating expansive soils are very general by nature. A lot has to do with the type of clay mineral, the environmental effects and so on. It is important to look at 4% swell as being in the upper range of "low" swell and close to the lower range of "moderate" swell.

In relating swell to expansion index, one could say 4% swell is same ase Expansion Index of 40 which is "Low", i.e E.I. value between 20 and 50. If you were to run ASTM 4546, like Irawan suggested, I suspect you would get swelling between 2 and 4 ksf, based on my experience with CA soils.