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Frost Depth at Descending Slope 1

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waytsh

waytsh

Structural
Jun 10, 2004
373
I have a footing where there will be a descending slope adjacent to my grade beam. The grade will never fall below the bottom of the footing but I want to make sure they grade around the footing properly to protect from frost. Here is the detail I am planning on showing. Is there a better way to show this? I have not designed the footing yet so you can ignore all the other information at this point.

Frost_at_Slope_mjes8c.jpg


Welcome your thoughts. Thanks.
 
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If the frost depth 3' , you may consider the blinding layer also. However, IMO ,the picture is conservatively O.K.
 
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you need to indicate how far away from the footing to take this. up to 3 feet away from the footing? what if the slope extends for 20 feet away from the footing, are you still requiring the 3 feet dimension?

IMG_4091_wmy7pu.jpg
 
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To piggyback off this post, how does frost heave actually work? Where does the water come from and why is it better to put your footing below a certain line?

I've been designing frost-resistant footings for a decade and I never thought of this until I saw this post.
 
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Moisture retained in the cells of fine clayey soil. That's why you don't want to dig in the yard during the winter.
 
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Thanks for all the input. Yes, the frost depth is 3'-0".

cvg, do you think this is more clear?

Frost_at_Slope_a9xnqy.jpg
 
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well, i doubt that the slope will ever be vertical, so no that is not any better. i think a horizontal dimension would be more clear
 
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For right triangle, the hypotenuse and the leg can't be both 3'. You should eliminate one. I suggest to increase and keep the vertical distance, so the 3' requirement is met when measured normal to the slope. Practically speaking, I'll keep a flat bench next to the grade beam, for easy/better compaction and retention of the soil.
 
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The criteria should probably be that you want 3'-0" minimum from the bottom of the footing to the grade. If so, the first detail was the best. If there is any doubt, you can always add a bit of insulation.

BA
 
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I don't know how much of a bench could be located. There is a parking lot about 8' away from the edge of the footing and 42" below finish floor.

Would the insulation need to extend all the way up to finish grade and be visible? Or would we be able to conceal it under grade a bit?
 
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No! Yes! Just provide the equivalent of 3'-0" earth cover assuming one inch of Styrofoam is equivalent to one foot of earth. See below.

image_qu3dil.png


BA
 
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Thank you BA, that is a good suggestion.
 
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If your slope is 42" over 8', then I show the bottom of the footing being 2'-9" below grade (perpendicular to grade) when finished grade is 36" above the bottom of the footing. If possible, could you just specify 3'-6" minimum (vertically) to make it easy for the guy in the field, either by raising grade or lowering the bottom of footing?

"You don't know what all you don't know, until you don't know it.
 
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Pardon my ignorance but in "grade 6" below F.F" what is "F.F." ?
 
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F.F. stands for finish floor. Typically in plans, elevations are called out with respect to finish floor elevation, which is set to 0'-0". So grade 6 below FF probably means finished grade to be -0'-6" below finished floor elevation.

"You don't know what you don't know, until you don't know it.
 
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Good question. I was confused until seeing explanation provided by 8-of-Trades.
 
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