Does Perc. test determine frost depth?

intelijoc · February 01, 2011, 09:10:04 AM

Does the percolation test reveal the frost depth? I ask because my understanding is that in colder climates like (Colorado) a footing needs to be at least 1ft. below frost depth.

cbc58 · February 01, 2011, 10:03:42 AM

don't think so. a perk test is different from a "test pit" where they dig deep-down with a backhoe (at least in new england). perk test is for drainage / absobtion testing - test pit is for soil classification and to determine where the seasonal high water table is. think that's right.

February 01, 2011, 10:14:18 AM

No. But I wonder if septic systems need to buried deeper where the frost depth is deeper?

intelijoc · February 01, 2011, 10:17:22 AM

So I need a "test pit" test to determine frost depth before I can determine depth of footings?

cbc58 · February 01, 2011, 10:24:48 AM

no - just ask any foundation contractor or builder in your area - or just google it.

February 01, 2011, 10:43:27 AM

Right, the building/permitting department will know. And while at it you could ask about any special things they will want regarding termites and what snow load to build the roof for...

Alan Gage · February 01, 2011, 11:43:55 AM

Quote from: MountainDon on February 01, 2011, 10:14:18 AM
No. But I wonder if septic systems need to buried deeper where the frost depth is deeper?

No. Maximum frost depth here is normally 3-4'. The maximum leach field depth (bottom of trench) below grade is 3' and they prefer 2'. The leach field needs to be at least 3' above the high water table.

The tank stays warm enough to keep from freezing and since there shouldn't be any standing water in the leach fields they don't worry about them freezing. If you run a long section of pipe from your septic tank to leach field I believe they want that to be frost protected but I'd think as long as the slope was correct it wouldn't be a problem.

intelijoc - This should answer some of your questions:

http://www.eco-nomic.com/septic.htm

Alan

MountainDon · February 01, 2011, 12:06:02 PM

Thanks. Makes sense. My water table is measured in hundreds of feet

Squirl · February 01, 2011, 12:24:23 PM

Thanks Alan. That is very helpful. I've been looking for that exact answer.

intelijoc - you can get a good idea by Google image searching frost line maps for your state. Usually one of the first hits will be an official govt. website. Most states set the guidelines and are online. Going an extra 6 inches to a foot is never a bad idea.

CB - I was told by my county government that the 6ft test pit was also to determine what was below the absorption area for the perk. Example was if my soil perks at 3ft, but there a layer of bedrock at 4-6 ft, it would still fail.

Jeff922 · February 02, 2011, 03:43:29 PM

In general, if your soil Perks well than you are at less risk of frost damage. Frost related soil movement needs temps below freezing and moisture. Remove one or the other and the soil stays put. If the soil is very porous, like sand or gravely soil, it will perk very well. If your soil holds a lot of moisture, like clay, than err on the side of caution and go deep.