Removal of expansive soils under pavements

[Okiryu]

I have a new project which I have to deal with expansive soils... do you know any design approaches for pavement design in subgrades with expansive clays? I am looking for methods to determine the thickness of expansive clays to be removed in order to provide adequate support for this new pavement. The pavement will receive passenger vehicles and small trucks and some fire trucks.

 

[oldestguy]

Good luck. Depending on the degree of potential expansion or shrinkage (due to soil proprieties) about the best you might accomplish is some reduction in severity. Usually locals know about this in general. A factor, besides weather and amount of this soil depth with these properties, the added effect of trees can really raise heck with things, such as foundations lifting or settling. Walls opening to the outside, etc. On the subject of highways, much depends on what cost or other effect you can or can't tolerate as well as ride ability (hill and valleys in a once level road).. I frankly don't know of a pavement design procedure specifically set up to deal with this even after many years in the highway design field. For instance take the clays n Fond du Lac, WI. in some areas the shrinkage and expansion effect can go to 20 feet, commonly. No way to replace that. Usually design for loading and traffic is not related much to potential for shrinkage or expansion, but to strength factors, etc. Is this some sort of thesis project?? Otherwise locals usually have it well in hand, to some degree.

 

[Okiryu]

Thanks OG. In my area we deal with residual, non-expansive clays but this new project is at a new area for me and just learned that the project site has expansive clays. I am checking with a local Geotech but just wondering if anybody has any information about design guidelines for pavements on expansive clays. I am still searching on this...if I find something, I will update later. Thanks again !

 

[oldestguy]

OK. If new, why not give a call to the state highway dept main laboratory and see if any geotech supervisors (engineers) can help. Usually they are well into these things and for your job may help. They may even have a design procedure for this. One of my very early jobs was the head soil engineer for Wisconsin DOT (later they changed the designation). Always glad to talk with outsider engineers then.

 

[Okiryu]

OG, thanks again for the advice. Will check...

 

[MTNClimber]

I agree with OG. I'm sure different areas have different procedures. Here's a little of my experience.

In the Front Range Colorado, it's common for Town's and County's have their own codes for how to deal with swelling soils under roads.

Typically mitigation will depend on how expansive the material is. Swell/consolidation tests are run somewhere between a 200 to 250 psf surcharge load. Normally, mitigation by moisture treatment is required for anything over 2%-3% swell. At around 5% they want moisture treatment and chemical stabilization. Mitigation depths also vary between 1 and 3 feet.

Here's one example spec. I'll dig up more tomorrow when I have more time.

Aurora's Design and Construction Spec See Table on 5-13.

 

[Okiryu]

Found some documents:

On page 30 of the below document, there are some recommendations for overexcavation depths of expansive soils based on PI. This is from Colorado DOT.

https://www.codot.gov/programs/research/pdfs/1992/expansivesoil.pdf

Other good general info here:

http://railknowledgebank.com/Presto...mnt=VHJ1ZQ==&uSesDM=False&rIdx=MTE0NDY=&rCFU=

Here is an extensive report from Texas A&M (haven't go thru it yet):

https://static.tti.tamu.edu/tti.tamu.edu/documents/0-4518-1-V1.pdf

https://static.tti.tamu.edu/tti.tamu.edu/documents/0-4518-1-V2.pdf

 

[MTNClimber]

Here's the most recent CDOT Pavement Design Manual. On page 186 they discuss expansive subgrades. Page 190 talks about stabilizing for expansive subgrades.

 

[fattdad]

Our program (Virginia) requires that he soils within 3 ft of the subgrade show CBR swell less than 5 percent. The implication being that we don't want, "Expansive" soils in that upper 3 ft.

I'd see of Colorado has similar programmatic constraints.

f-d

ípapß gordo ainÆt no madre flaca!