when to ignore frost depth? 1

can someone who has more experience with frost depth clarify if an equipment foundation does not need to meet frost depth

"Frost - free footings may not be required for a temporary structure that meets therequirements of the state building code unless required by an engineering report.Temporary electrical and plumbing installations may be allowed for any structure by thegovernmental entities governing those areas of construction or the applicable codes."

Is the equipment sensitive to movement? If so, then you will want to avoid frost heave. Is it a temporary structure? I assume that is an excerpt from your geotech report?

As mike noted... need more info. What is soil, is it frost heave susceptable. You can make a structured slab with piles and void form below, or you can put insulation down, likely extending 6' or so beyond the slab so that the soil beneath doesn't freeze. We're a little further north of Minnesota and deal with frost all the time.

Dik

I don't even have soil report. This is an existing site and client just want to add equipment. Well there are piping connected to this equipment.

Dik, what other options do I have? Can I put insulation on the side and below the slab. Slab is 16'x12'x1'-6" thick, 1' below grade. I don't want this to be complicated.

Just to be clear, if a structure is by "engineering judgment" not sensitive to movement, I can ignore the frost depth of it's foundation.

I think this is a good reference. I'll just figure out the frost depth. Which can be confusing because the soil may not be susceptible which I don't know without geotech. I'll call engineer's office first.

Or, add suitably rated hose or pipe expansion loops at the periphery of the slab, so even if the slab moves, the pipes won't be overstressed.
Similarly for electrical connections.



Mike Halloran
Pembroke Pines, FL, USA

good point mike but I think piping will just tell me to make sure my slab don't move instead of doing that

piping will just tell me to make sure my slab don't move

Click to expand...

Tell them to move it to Georgia.

No way is a slab in Minnesota not going to move, someday.



Mike Halloran
Pembroke Pines, FL, USA

<edit>
Make that _south_ Georgia, or Florida.

How does the other equipment behave in winter? If it does not have problems sitting on a slab, you may be OK. If you want to minimize heaving, one easy remedy is to dig down a few feet (not necessarily to "frost depth") and replace that with compacted clean granular material, such as that used as aggregate for concrete, frost heaving will be much less, if at all.

This funny common term "frost depth" gets thrown around a lot and at any specific site it may be way off. Let's say frost depth means where the temperature can go down to 32 degrees F. That doesn't necessarily mean in that zone there will be heaving. Three things needed for heaving: Cold below freezing, water and soil with fines in the silt range that tend to expand and take on water when below 32 degrees. That last part is a complicated activity that let's not try to explain here. When you have plenty of water and that frost heaving type soil you can get major heaving. But reduce those factors and the heaving is less. For that clean granular material with barely any silt no heaving takes place. An interesting fact is that if you have plenty of water, the heat of fusion released as freezing takes place, minimizes the depth of freezing. Minimum depth of freezing is in a lake while on shore it can go deeper. On the other hand take that clean granular material for deep depths and temp can go below freeing many feet deeper than for silty ground and no heaving. Also ground surface material can insulate the deeper soil to some extent and reduce the depth of freezing. As an example no frost heaving takes place in many areas of LaCrosse, WI where I have measured below freeing temps at 10 feet depth in mid December. It's all clean sand and gravel there and deep to water. So "frost depth" there is a meaningless number. Sorry, I sometimes tend to preach.

yes, oldestguy, i'm aware that 3 things are necessary for frost heave: 1) the soil is frost susceptible (large silt fraction), 2) sufficient moisture is available (soil is above approximately 80 percent saturation), and 3) sub-freezing temperatures are penetrating the soil. Removing one of these factors will negate the possibility of frost damage.

i will definitely add compacted granular base material below the foundation.

OG again: Having spent some time in Wisconsin DOT a comment on your statement of the undercut and granular material. Be careful with the word "base". A contractor may bring in roadway base course material. That may be OK but some specs allow a lot of P-200 sieve material in base courses. I've seen some pretty bad base course conditions in the spring of the year due to too high a silt content, For the small quantity you will need I'd ask for a mix of fine aggregate and coarse aggregate for concrete (from a ready mix plant) meeting ASTM C-33. A typical mix is one part sand and two parts coarse aggregate.

oldestguy - noted. I'm thinking using 6" thk aggregate, 4' beyond the slab. there is a guide to calculate this but it's not really exact science.

also I'm not sure if the insulation I will put is effective since there will be piping and electrical conduit coming up from the side of the slab penetrating the insulation.
I'm thinking of not putting insulation at all and just use aggregate below and beyond the slab.

Delagina:
But, it still seems you are way short of needed engineering info. and maybe sorta missing the point of some of the comments above. If it is an unheated, uninsulated, enclosed bldg., or an open bldg., or basically a slab on grade, the insulation really doesn’t do much good, up in that neck of the woods. You will have frost under and around the slab, and possible some movement. The point of the insul. around the found. and maybe even extending out horizontally 3-4', a foot below grade, is to retain bldg. heat and ground source heat under the found. and prevent freezing. Alternatively, if it is well draining soil (sand, gravel, etc.), and a well drained site, low local (perched?)water table, water drains away from the slab (or bldg.) a sufficient distance, etc. the frost heaving problem is likely significantly diminished. One solution is to put these slabs at a high spot on the site and have the top of the slab be above a sloping (away) grade, not at a low spot or dug a couple feet into the ground, like a bath tub.

What type of equip. is this, how does it load the slab, and can the equip. take some of this movement, work out-of-level, etc. The slab can be made strong enough so that any movement of the slab and above will be a rigid body movement, but then can the piping and its connections to the equip. tolerate this movement. That’s a pretty good sized slab so you must be talking about some sizeable equip. Is this in conjunction with a pipeline, a compressor bldg. or some such? Does it produce enough heat to heat the bldg. and found. adequately? Is the pipeline contents heated? The pipeline should be designed for these kinds of things, how is this potential movement handled at other similar locations on the line?

Do a search for DOW foundation insulation.

Dik

i plan on doing something like this, which is what is recommended for unheated or unenclosed slab on grade..

Something like the attached.

Just noticed... that should be extruded polystyrene...

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1501680735/tips/Section_ocjauc.pdf[/url]

The section assumes the space is heated. For anchors I usually use headed bolts. They work better than 'J' bolts and are less costly.

Dik

dik: That detail probably is for a heated building. Cold (heat loss) follows the easiest path and in that case it goes via the slab when unheated.

OG... Yup...

Dik

and another one... for unheated...

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1501690834/tips/Sections01_esix8q.pdf[/url]