×
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

When is a pile too short?

When is a pile too short?

When is a pile too short?

(OP)
When designing piles/bored piers for lateral loads what is the limiting depth at which it ceases to behave as a laterally loaded pile and instead behaves as a spread footing? Is there a minimum embedment depth as a ratio of the pile diameter?

RE: When is a pile too short?

It depends on soil conditions and the depth of embedment needed to achieve pile fixity to resist the lateral load/moment.

Run L-Pile or do hand calcs using a variety of different soil strata and you'll see.

RE: When is a pile too short?

(OP)
Pile design methods assume that the lateral resistance comes from bearing on the sides of the pile with lateral displacement of the soil, i.e. the predominant pile movement is sideways. However near the surface the soil will fail in a simple passive failure wedge with much lower pressure. Also the pile will tend to rotate about the base like a pad footing. So my question is really where does the transition from pile behaviour to pad footing behaviour begin?

In my particular case because of design considerations we are using vastly oversized piled and loads are small. We have a 3m x 2.5m plan shelter and we are using 750mm diameter piles. Using the Brinch Hansen method (BHPile) the calculated pile depth is only about 1 diameter. I suspect the method and the software are not appropriate for these conditions but I can't find any reference to say what the validity limits are.

RE: When is a pile too short?

We need to determine if you have a circular shallow foundation or a rigid drilled pier. You may have to analyze it both ways. Jumikis's 2nd ed. "Foundation Engineering" book covers circular foundations. The 5th ed. Bowles book and also the '88 Reese & O'Neil manual on drilled shafts both recommend that the deflection at the pier tip be very small. I prefer to increase my drilled pier embedment until I reach a deflection of less than 1 mm at pier tip. Then I check lateral bearing pressure, settlement & axial capacity.

http://www.soilstructure.com/

RE: When is a pile too short?

Just run some lateral force analysis for the pile with using either LPile or PileLAT 2014. No other quick ways apart from that. This is simply because the minimum pile length depends on the loading, soil types and strength and the pile top boundary conditions. It is up to the design requirements such as maximum allowable deflection at the pile head, maximum bending moment or shear force mobilised in the pile under the lateral force, etc. Having said that, you can use 10 times pile diameter as a good starting point.

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