Design for Lateral Capacity of Rigid Piles

[tmitchell]

I need to determine the maximum moment and its associated location for a laterally loaded 4-foot diameter caisson in a cohesive soil. The caissons are approximately 50 feet long and bear on (embeded 5 feet) a very dense layer. With the relatively large diameter, compared to the length, the pile is classified as a rigid pile.

The problem that I am running into is that all information, that I have, has equasions and associated coefficients for "long" piles.


Could someone help me with how to go about addressing a rigid pile?

 

[ishvaaag]

Piles under lateral load are well protraited in

Foundation Analysis and Design 5th Edition
Joseph E. Bowles
Mc Graw Hill
Chapter 16 and 18

If you have charaterized the lateral response of the soil (enough to provide lateral springs for your model) you simply have to make such model. Variation of the input parameters will allow you to bracket the likely range of behaviours. For this purpose I sometimes have used 1/2 to 1/3 of the vertically expected modulus of subgrade reaction.
The fact of the soil being cohesive may be dealt in this kind of model by lower stiffness of the soil longterm; in proportion to the secondary compression respect the primary should be a good guess, I muse.

CRSI as part of its 94_2nd combo of 4 programs have Latpile program by Robert L. Cararie, precisely for rigid piles (limited there to slenderness=10) but since assumed to rotate freely within the soil it is unlikely can model your higher lateral fixity at bottom.

I think there's other LATPILE program and alike derivations freely available by some transportation organizations.

 

[72shortbox]

try using a program COM624P you can input a soil profile, pile dimentions and a loading. It will calculate the moment at every incremental depth. You can get the program free at

http://www.fhwa.dot.gov/bridg/geosoft.htm