outdoor equipment pad
outdoor equipment pad
(OP)
Those of you practicing in northern climates, do you typically worry about frost around the edges of an equipment pad that will be installed outdoors? The pad I am designing needs to be at least 8" thick to get all the rebar in, but I am wondering if I should turn down the edges of the concrete to a deeper depth. The pad is about 8' x 10' in plan size. Normal depth of footing around here to prevent frost heaving is 3'. What is the practice in your office for this type of situation? Yours truly is not asked to outdoor design equipment pads very often!






RE: outdoor equipment pad
RE: outdoor equipment pad
To prevent heaving beneath utility pads on grade we usually either hire a geotechnical engineer to check the soil to see if it is frost susceptible, or excavate and replace with a granular, non-frost susceptible material of sufficient particle size (gravel, crushed stone)to a depth equal to the depth of frost dictated by local authorities. Turning down the edge of slab will not mitigate the movement unless the pad is designed to span and resist the uplift forces from frost.
RE: outdoor equipment pad
Fyi, the pad is completely unprotected from the elements. Subgrade below it will definitely freeze at some point. Perhaps turning down the edges is a bad idea- if as wsiladi notes there can be uplift on the pad interior because only part of the supporting subgrade freezes. I am also hesitant to make a prediction about the magnitude of uplift pressure resulting from freezing soil.
I was planning to require proof rolling of the subgrade and a 6" layer of crushed stone under the pad. Perhaps I may make the stone layer deeper to promote drainage, and provide some resiliance (ie pore space) for absorbing upward forces as noted in the posts above.
There is not much geotechnical data available at the site, all I have is an allowable subgrade pressure of 2000 psf. This is a small project (Its mostly changes to an existing building), so there is no budget for a geotechnical investigation.
RE: outdoor equipment pad