Geofoam under foundations

[Bill13214]

I've heard of using geofoam under roadways and embankments, but can they be used under building foundations?

 

[Jalthi]

For what purpose?

 

[Bill13214]

To avoid a very costly overexcavation of unsuitable soils of the manitude of 10 - 15 feet.

 

[Ron]

yes...It can be used under buildings

 

[oldestguy]

I have polled the same question at another "room" that is access restricted. I was looking for cases. None could be found as to being used under foundations.

I have used the stuff under the basement floors of two houses that I have had built and no problems. Makes for a comfortable basement.

If you look at the crushing strength of the stuff and then go well below that pressure, it would seem it would work, but why be the first to do it?

I did that very thing for a cellar door area way wall foundations for my present house. So far so good, but we will see if the winter changes things. The purpose was to avoid going below that mystical thing called "frost depth".

 

[hokie66]

Isn't 'geofoam' just expanded polystyrene? The last time I checked, the cost of polystyrene by volume was about the same as concrete. Unless reduction of mass is what is required, I imagine some of the liquifil products would be preferable for mass filling. Maybe I have misunderstood...how does the use of 'geofoam' alleviate the need to excavate unsuitable soils?

 

[Ron]

hokie66...I believe he is referring to cellular concrete material ("foamed" concrete).

I would have the same question...filling with this material, even though it might have a higher modulus than typical soil, won't help if you have poor soil conditions below....though it will likely reduce the loading on the poor soils if used to replace some of the existing overburden.

I would look at overexcavating the site to remove the soils or consider deep foundations.

 

[moe333]

I have seen its use in a "compensated foundation" whereby existing fill was removed and replaced with the geofoam to reduce the load on underlying compressible soils (to reduce building settlement) - very similar to a preload/surcharge.

 

[Bill13214]

The issue is partially controlled and partially uncontrolled fill placed over the years on an existing slope to a maximum depth of 20'+/-. The idea is to reduce the load and therefore reduce potential settlement. I'm not convinced that this is an appropriate measure below a building.

 

[aeoliantexan]

Bill: The problems I have seen with uncontrolled fill usually involves loose fill that compresses when water gets into it. If the fill is saturated and can be considered to be normally consolidated under the existing oveburden, using geofoam or lightweight aggregate to compensate for the new loads should work. If the fill is still dry, it is just waiting to become a problem some day.

Moe: We are considering doing what you described under a process building and some tanks for a small water treatment plant on a site with deep compressible clays. I am concerned about contact settlement due to imperfect bedding of the geofoam on the soil and between layers of the foam. Did you do anything special to address this issue?

 

[moe333]

I wasn't directly involved in the project so I am not sure what special procedures may have been used. I would think slow and strategilcally directed (and inspected) placement of the geofoam may help to reduce voids that could later result in settlement.