×
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

LRFD Driven Pile Design

LRFD Driven Pile Design

LRFD Driven Pile Design

(OP)
thread256-229716: AASHTO LRFD Driven Pile Estimated Length

In reference to the above thread, if we use phi(static)=0.4 to determine the length of the pile and during construction use dynamic testing phi(dyn) =0.65 the production pile lengths will be one third shorter and will invite claims from the contractor because the change in quantities is greater than 25%. This is the standard practice for the state agencies we work for. Furthermore, if we use phi(dyn) = 0.65 and depending on the psi load factor we use to calculate the factored load the equivalent factor of safety is equal to 2.0 which is similar to the factor of safety we generally use in ASD pile design with dynamic testing. If this is not the case what is the relationship between phi(dyn) and phi(stat)?

RE: LRFD Driven Pile Design

I think you are making the assumption that a static analysis and PDA analysis should give you the same length for a pile. However since the static method is less reliable, it will give you a longer pile length to achive the same load as a PDA test if the soil conditions are exactly as predicted. Since this is rarely the case, properly done static analysis by practioners experienced in the subject soils and PDA test may be much closer than you are predicting. Or not. Static analysis is a rough guess. I am not a fan of the methods ASSHTO uses for static analysis. Really the idea is to give you a good place to start with your pile test program. Note that bearing capacity is only one aspect of pile design. settlement, lateral loads and group effects need to be considered. In short that there is so much variation in soils and the static analysis is so different from PDA that you can not assume that both methods will get you to the same answer.
Final note under ASD, static load test were given an FS of 2 while dynamic testing generally was about 2.5 and staic was 3

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