Frost Protection - Ag Structure

[jchi]

Question concerning agricultural code requirments? I am designing a mat foundation(14'x24'x18" thick) (12" below grade) in Iowa supporting a grain bin and head house on a 10'x20' steel framed structure. Frost protection required depth is typically 42" in this area. The structure can tolarate movement from frost... Do I need to pour the entire mat 48" thick or thicken the edges to 48" and insulate below center area?

 

[steve1]

Not sure what the code agricultural requirements are for frost protection, but here in the northeast I specify excavating to the frost line and backflling with a compacted, non frost susceptible soil to the underside of industrial slabs on grade. I have used this technique for slabs of 6" to 24" thickness.

 

[dik]

I've generally used insulation located about 12" below grade to protect against UV degredation... Typically a 24" dp edge... this permits insul thickness, 6 or 8" from grade to structure and 12" soil protection.

Dik

 

[slipstick50]

Before starting any design or constructon, get a soils test done. Generally, overexcavate per the soils test recommendations and backfill and compact per recommendations.. Work with the soil test engineer and consider drain tile at the bottom of the backfill.... pay alot of attention to drainage and keep water away from the site even when over excavated and backfilled properly per the test report.

 

[oldestguy]

For sepcifying non-frost susceptible soil, I have simplified the rules by Terzaghi and others by saying: "Of the fraction that passes a Number 4 sieve, no more than 5 percent may pass a Number 200 sieve."

Keep in mind that this granular soil will naturally retain much less moisture than the silts or clays of Iowa. The more moisture, the lesser the "frost depth". You remember that high school physics class about heat of fusion?

Therefore, if they say frost depth is 42 inches, (assuming in their silts and clays), you would be wise to go deeper with an undercut that is backfilled with non-frost susceptible soil, compacted of course. 48 inches would be my least deth recommendation, butI have seen frozen ground in Wisconsin, in December, 8 feet below grade in clean sand.