outdoor sport court frost heave protection 2

[DoubleStud]

We have a project where they will build a sport court outdoor. The frost depth is 4 ft deep. The slab will be post tensioned slab on grade. I am just wondering what would be the best way to protect the slab from frost heave. They want this sport court to last for a long time. At first I thought they just wanted to do a typical outdoor slab on grade where movement does not really matter. The soil report suggested using 3 ft deep of structural fill. I was just wondering if I have other options perhaps using rigid foam or maybe concrete apron wall around the perimeter of the court that goes frost depth?

 

[Once20036]

Here are some of my old thoughts on the topic:

https://www.eng-tips.com/viewthread.cfm?qid=441716

I don't think that there's any amount of insulation that would help in your instance, because there is no source of heat. The insulation will just slow down the cold transfer. If your frost depth is 4', I assume you have a long winter and the cold will eventually win.

Otherwise, I like the "non frost susceptible fill". I think it`ll be way cheaper and more durable than a concrete apron wall.
If you use the wall, the first time the slab cracks and water can seep through, the wall becomes totally ineffective.

 

[canwesteng]

Unless you're in a permafrost area, the source of heat is the soil (well the sun in the summer). Essentially the insulation slows down the rate of heat loss in the winter, so that it doesn't freeze, and the soil heats back up in the summer (slowly).

 

[CarlB]

The thread referenced by Once20036 has some relevant ideas. But I disagree with the premise about no benefit to insulation. Slowing down the frost is exactly what reduces the frost depth, as there is a limited "freezing index" driving the frost. This approach is basis for insulation of unheated structures in ASCE 32 and is principle of pavement insulation techniques commonly used in cold regions.

The frost wall would be of limited benefit, doesn't affect the thermal regime, or prevent moisture migration from below.
Thermal modelling shows 1" of insulation has thermal benefit of about 2 feet of soil, in regards to limiting frost penetration.

So one possible scheme would be to place about 6" non-frost susceptible (NFS) material (clean sand/gravel, then 2" rigid insulation, then 12" additional NFS, and place slab over that.
Frost may penetrate a small amount below insulation, so good to have some NFS below, and for levelling.
Thin fill over insulation not easy to compact, thus 12" suggested.
Other schemes are possible, such as insulation directly below the slab. Then should provide say 12" NFS below.
And extend NFS fill and insulation beyond perimeter of slab, 3 feet should be plenty.

 

[DoubleStud]

Thanks CarlB, is there something I can read somewhere about this? I dont want to reference an eng-tips thread .

 

[Brad805]

Piles?

 

[dauwerda]

Thanks CarlB, is there something I can read somewhere about this? I dont want to reference an eng-tips thread .

ASCE 32, Design and Construction of Frost-Protected Shallow Foundations

https://ascelibrary.org/doi/book/10.1061/9780784405642

 

[1503-44]

Good surface drainage is the easiest way. Make it easy for water to run off horizontally and it won't do down. Sand bitumen mix. Plastic geo liner below that. Similar to right side of this detail.

http://vastapad.com/wp-content/uploads/2018/03/Section-1.jpg

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[dik]

4" or so of rigid polystyrene insulation, extending out 4' around the edges. Check with DOW; they have a really good manner of calculating the thickness and extended part...else live with whatever movement takes place... and perimeter drainage will likely help.

I'm not so sure about clean gravel. I've done reports where clean stone has water and this has frozen and caused heave. It would have to be well drained. Insulation works by having the geothermal heat from the earth to come to near the surface and the insulation works also by preventing the cold from going below it.

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1677279170/tips/0901b803801f6296_blgmyp.pdf[/url]

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1677279170/tips/DOWInsul_aocr9v.pdf[/url]

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[CarlB]

Some guides that that should have similar methods as ASCE 32:

https://www.huduser.gov/publications/pdf/fpsfguide.pdf

https://www.homeinnovation.com/~/me...de-to-Frost-Protected-Shallow-Foundations.pdf

Any soil that is fully saturated can heave some, as water expands 9% when changing to ice phase. Is best to prevent frost from extending to the groundwater table, below structure. NFS soils (by definition) should not wick water, nor allow ice lenses to form.

 

[dik]

thanks, Carl...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik