Return to index: [Subject] [Thread] [Date] [Author]

Re: Bottom of footing depth

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Albert,

	There are two problems which can arise from placing footings on frozen
ground; the change in volume of the sub footing material due to water
changing to ice may cause movement, mainly differential movement, of the
structure; and if the material is frozen prior to placing concrete it
may cause the concrete itself to freeze prior to curing and hence
prevent curing of the concrete (this was discussed several weeks ago on
this list).

	It follows that if the frost line does not reach the water table AND
you have a free draining material, like sand or gravel, that is not
susceptible to volume changes upon freezing you can place your footings
at any level you want.  Under most other soil conditions you should have
the underside of your footings below the frost line.

	Of course, if you don't care if the structure does move up and down
with seasonal changes in the soil you can also put the footings at any
level you want.  In any case you should not allow the concrete to freeze
before it cures.

	As an alternative, you can always provide ground insulation or maintain
a heated structure to artificially keep the frost line above the
footing.  This is an engineering solution which is applied quite
frequently in Canada.

	I hope this helps.

				Regards,

				H. Daryl Richardson

> Albert J. Meyer, Jr. wrote:
>
> Sorry if this is a repeat, I don't think that the server at work is
> working properly.  I know that some place the minimum bottom elevation
> of footings at the frost line.  I know of others who place the top
> of footing elevation at the frost line.  Any opinions on this?  It
> seems reasonable that if the bottom of the footing is at or below the
> frost line then you wouldn't experience adverse effects due to soil
> freezing, but given the differing opinions, I'm no longer sure.
> Thanks in advance for your response.
>
> A. J. Meyer, Jr., P.E.

******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
*
*   This email was sent to you via Structural Engineers
*   Association of Southern California (SEAOSC) server. To
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
*   send to the list is public domain and may be re-posted
*   without your permission. Make sure you visit our web
*   site at: http://www.seaint.org
******* ****** ****** ****** ******* ****** ****** ********