Frost depth consideration in case of refusals

[Gaurah]

Dear all,
In case of foundation design, steel pile and concrete pier embedment is kept larger than frost depth.
How does one approach a situation where refusal is encountered, even before frost depth is reached.
Is it fine to keep foundation at lesser depth than frost till it is fine in uplift and lateral deflection. (In case of refusals)

Avdhesh

 

[oldestguy]

What do you mean by "refusal"? STP results? Excavstor can't go deeper? Bedrock? If bedrock, usually that does not heave, so you can use shallower depth of footings.

 

[jayrod12]

but what about frost heave from adfreezing grabbing the sides of the pile and popping it out of the ground. I'd be inclined to be more worried about it.

 

[Gaurah]

Yes. i meant that pile driving machine cant go further as hit a hard bedrock.
I have same question further as jayrod12, "what about frost heave from adfreezing grabbing the sides of the pile and popping it out of the ground. I'd be inclined to be more worried about it."

Thank you for your prompt response.

Avdhesh

 

[jayrod12]

Something I might be just as worried about, if you are hitting refusal before you are reaching the projected frost depth then are your driven piles still acting correctly? they won't have the same lateral confinement when they are only 3m into the ground as if they were 10m.

 

[Gaurah]

@jayroad, Yes i would not go with a depth that does not go well at lateral or downward push or uplift. In few cases, my post is good at all 3 conditions at shallow depth but I have to go further deep embedment for frost consideration. My concern is whether I can still stay good for steel post if i hit refusal above frost depth (Given all 3 load cases, uplift, push and lateral are fine at that shallow depth).


Avdhesh

 

[structSU10]

could you just put some epoxy dowels into the rock to help hold it down for this sitation? Just a guess really, don't know how realistic it even is to try and resist frost heave forces.

 

[manstrom]

Get the geotech to approve it. Dowel into the bedrock.

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

 

[Gaurah]

This helps a lot.

Thank you
Avdhesh

 

[jayrod12]

The adfreezing force is huge (particularly on steel) If I remember correctly the Canadian foundation manual has it in the range of 250 kPa as a worst case. Concrete it is much lower than that.

 

[oldestguy]

Another question. What is "frost depth"? In my neck of the woods, if the ground is fine grained, silty and with clay, the high moisture there usually means shallow depth of freezing. On the other hand, if the soil is relatively clean sand, the depth of freezing can be many times what happens in more silty or clay like. This range around here (Wisconsin) can go from 2 feet to over 8 feet down. Then comes another question: which soil will heave? The "dirty" stuff will heave,while the clean sand won't. The local terms of Frost Depth usually come from a building code and may or may not apply to your job.

Since the depth of freezing, depends on water content, all other conditions the same, where is the shallowest depth of freezing "Frost Depth"?

Answer: a lake.

Be careful throwing around "standard" terms.