×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

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!

*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

Transmission Tower Deep Concrete Foundation in Soft Clay

Transmission Tower Deep Concrete Foundation in Soft Clay

Transmission Tower Deep Concrete Foundation in Soft Clay

(OP)
An outside engineer firm is proposing a 10' diameter by 49' drilled shaft in soft clay soil. Using the geotechnical report, the axial load resistance is 266 kips. The pole supported has an axial load of 58 kips, but the foundation alone weighs 577 kips. This raised some flags for our engineering staff so we asked they provided supporting calculations, they answered with this:

"Note that the mass of concrete is displacing the in situ soil that will be removed and therefore only the net increase in mass need be considered. This net difference plus the axial load imparted by the pole can resisted by skin friction."

Is this an acceptable assumption? Other resources I've been able to find are for piles, and don't specify the type or diameter.

RE: Transmission Tower Deep Concrete Foundation in Soft Clay

Yes, that is a reasonable assumption, assuming that's what the geotech report allows. If 266k were the total capacity the soil couldn't support its own weight.

The weight of soil displaced by a 10' diameter by 49' drilled shaft (assuming 110pcf, no water table, etc., so probably wrong) is 423kips. The difference is 154kips. Add in the 58kips for the pole for a total of 212kips, which is less than 266k. This is assuming that the 266k is allowable capacity, with safety factors already built in. If it's ultimate capacity, then you'll have to apply a dead-load factor to the 154k.

RE: Transmission Tower Deep Concrete Foundation in Soft Clay

jwk is right on -- in nearly all geotechnical reports, the allowable foundation load will be presented not including the weight of the foundation (below grade) -- precisely because the geotech doesn't know the final dimensions of the foundation to be used, and doesn't need to know.

----
The name is a long story -- just call me Lo.

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! Already a Member? Login


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close