×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Lateral resistance and frost depth

Lateral resistance and frost depth

Lateral resistance and frost depth

(OP)
I'm working on an analysis of an existing drilled shaft in SM soils (frost susceptible), where overturning is the governing criteria, not end bearing.

The existing drilled shaft terminates 9 feet below ground surface and frost depth is 5 feet below ground surface. When I neglect lateral resistance below frost depth this foundation is failing, big time.

I'm afraid to recommend removing any existing soils to place an "insulating" layer of materials less susceptible to freeze-thaw/seasonal variations, because 1) there is an existing structure adjacent to the one I'm considering. 2) I'm concerned that removing any existing soils would worsen the conditions and reduce my lateral resistance.

All of my resources specifically say that you should bear below frost depth, which this criteria has already been met. Does anyone have any reliable/credible resource(s) that includes soils above the frost depth for lateral resistance?

Intuition tells me that there should be some resistance, though it should probably be reduced. Thanks.

RE: Lateral resistance and frost depth

I assume you menat "when you neglect lateral resistance ABOVE frost depth"...

When thee soil is frozen, strength and lateral resistance is generally much greater than when thawed. After thawing, and any excess pore water pressure dissipates, the soil returns to essentially the same strength (possibly some decreased density/strength in upper foot or so.) The worst case (for a particular layer/depth) is as the soil is thawing, if it had formed ice lenses when it froze, as it can temporarily lose a lot of strength. Hard to say the worst case for lateral resistance, depends on the rathe of thawing versus moisture dissipation, and there is some incresed capacity from the soil that remains frozen.

My experinece (in Alaska) is that reduced lateral capacity is rarely a concern.  Frost jacking is what usually causes problems for posts/piles. You might consider placing board insulation (say at 1'-3' depth), which would reduce frost penetration, help lateral somewhat, and help resist jacking.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources