Deck & gabion wall foundation on helical piers & frost heave

[RattlinBog]

I'm designing a standalone wood deck overlooking a lake. I also need to support a decorative, rock-filled gabion wall next to the deck (about 750 psf/ft). Soils are poor for 30+ ft, so I'm planning on helical piers for gravity and lateral. I'm in a 5 ft frost depth area.

See sketch below. I'm concerned about frost heave on the continuous footing that is supporting the long gabion wall and the back end of the deck. Has anyone found an elegant solution for something like this?

I see a few options:
1) thicken footing to bring bottom down below frost (5 ft below grade) - would rather avoid this...likely expensive and fighting high water table
2) provide insulation around/below footing and extend horizontally in an attempt to prevent frost from reaching footing
3) provide void form below footing to sacrificially crush under frost heave forces
4) do nothing and assume helical piers are able to resist frost heave - I don't believe this is true because frost could still grab the concrete surface

 

[jayrod12]

for a piled foundation we regularly provide void form underneath of the beams to prevent frost heave. So that solution would likely work for you.

 

[W460x68]

I will always provide void form for pile foundations where the grade beam is not below frost depth.

 

[RattlinBog]

Thanks for the feedback. I'll plan to use void form below the strip footing.

Came up with a slightly different concept below. Maybe I'll keep the deck independent of the gabion wall foundation. Support the deck on vertical and battered helical piers only. That way if the gabion wall foundation does heave at all, it at least won't take the deck with it. I'm less concerned about the gabion shifting.

 

[JAE]

1) thicken footing to bring bottom down below frost (5 ft below grade) - would rather avoid this...likely expensive and fighting high water table

FIrst and most sure way to avoid the heave but if you have a water table I understand.

2) provide insulation around/below footing and extend horizontally in an attempt to prevent frost from reaching footing

Usually do this when I have it near/under a heated building. Outdoors might be iffy as you are relying on the shallow earth to provide enough heat from below to avoid freezing. Might be OK but I'd want to research this a bit to ensure I'm not just delaying freezing and not denying freezing.

3) provide void form below footing to sacrificially crush under frost heave forces

Agree with others ... BUT ... void forms deteriorate away and leave an open void - the purpose of course - but then the adjacent earth can sluff down into the void over time and negate the void. In my south Texas days with expansive clays (similar to the freeze issue) we'd always you fill retainer planks around the perimeter of the footing to negate any sluffing. Usually 1 1/2" thick concrete panels - perhaps 18" wide - and leaned against the side of the footing and extended below the void about 4" or more.

4) do nothing and assume helical piers are able to resist frost heave - I don't believe this is true because frost could still grab the concrete surface

Agree with you that you'd have uplift - the question could be put to the pile manufacturer about uplift resistance but freeze uplift is usually thought of as an irresistible force.