Allowable Axial Pile N-SPT Safety Factor versus Allowable Displacement

[XFEM]

Hi, i am new here. I am designing deep pile foundation for building and bridge.

1. What allowable bearing capacity of deep pile is you more trust?

a. based on Empirical Safety Factors methods :alpha methods Excel AASHTO , or Meyerhoff N-SPT excel, SPT97 / FB-DEEP N-SPT Allowable axial with Davisson methods, and APILE. Usually Safety Factor is around 3.

b. based elastic allowable displacement methods pile software using winkler spring [Fb-Multipier, GROUPS] that not using Safety Factor.

2. Safety Factor for allowable capacity by CAPWAP? divide by 2.25 [AASHTO] or 2.5 [ASTM] ?

3. What the usually allowable elastic displacement/settlement for building and for bridge? I am only found the allowable horizontal displacement in AASHTO LRFD05 is 1.5in or 3.8 cm.
1cm, right?

 

[lovethecold]

It seems that this is a decision that should be made by your local geotechnical engineer. He or she should have the experience to know what works best in your area. Let them know what pile you are wanting to use and they can determine the allowable bearing capacity. Some states govern the type of pile that may be used (or is strongly preferred) for bridge design, this will affect the allowable bearing capacity.

Others can provide better guidance.

 

[DRC1]

Software and methods are two different issues. Typically I use alpha for clays and beta for drained soils. I use unified pile design theory as detailed by Candian Foundation Manual. Software by Unisoft.
Item b deals more with settlement wich I use more traditional elastic methods and is a seperate issue from bearing capacity.
Aashto now uses resitance factors so the coralation to traditional FS is somewhat blurred for bridges.
Allowable displacement would depend on the structure and is a matter for the designer, but an 1 1/2 inches of settlement seems like a lot for a piled structure.

 

[XFEM]

Yup, i usually check the allowable axial capacity just from unified formulas. When i check the deformation, i quite surprised.