Adfreeze on piles supporting concrete footing
Adfreeze on piles supporting concrete footing
(OP)
It seems clear to me that the upward heaving force develops in two ways: 1 frost heave pressure on underside surface of foundation, 2 upward adfreeze force on the side surfaces of foundation AND on the pile perimeter.
But when some engineers suggested that the afreeze on pile can be ignored when the frost heave pressure develps on the underside of foundation, I found I don't have strong geotechnical explanation to him.
Can somebody shed some light on this? Thanks,
j1d
But when some engineers suggested that the afreeze on pile can be ignored when the frost heave pressure develps on the underside of foundation, I found I don't have strong geotechnical explanation to him.
Can somebody shed some light on this? Thanks,
j1d





RE: Adfreeze on piles supporting concrete footing
They may be thinking in cases where the heave is surmised to be quite uniform, like when the ground take the piles along for an unheated foundation and moves everything up, piles, foundations and house. In these cases if the overall movement is uniform it may not turn very relevant to distinguish what part is coming from bottom and what from the sides, you would be thinking more than anything on the strong points' movement.
Yet you are right in that an incrusted item such a pile not directly able to take the same deformation than the surrounding soil will sustain mechanical efforts that in some cases may need to be characterized; and there's no other way without experience to say how much than trhough evaluation. So if the surrounding soil expands piles will be compressed concentrically towards their axes and will be subject to tension induced through friction along their axes. Friction may be overcome or even lost upon repeated cycles etc so in all there is a subject of interest in your question.
RE: Adfreeze on piles supporting concrete footing
Regards,
j1d
RE: Adfreeze on piles supporting concrete footing
RE: Adfreeze on piles supporting concrete footing
There is a 12" thick voidfoam under the pilecap (i.e. foundation). The design soil heave under the pilecap is 4", this is also the compression amount of the voidfoam. My point (to support the adfreeze on pile still existing) is the soil is not restrained by the pilecap rigidly. The soil under pilecap will move upward gradually up to 4". This still allows the adfreeze/friction on the piles to happen.
RE: Adfreeze on piles supporting concrete footing
Why is that? Isn't the pile also shrinking?
RE: Adfreeze on piles supporting concrete footing
There is also the issue of phase change in the water; the significant volume change of the water when passing to ice will be linearly something like 1.04^(1/3)=1.013000 m/m on a number of meters whereas say a 30ºC descent of temperature can bring on say a 30x0.000011=0.000330 m/m change on the size of the radius of the pile, this meaning that the free displacement towards a void of the frozen ground is 2 or 3 orders of magnitude greater than the ability of the concrete to shorten under the temperature descent, hence leading to a compression field on the perimeter of the piles.
RE: Adfreeze on piles supporting concrete footing