Design of Pile Supported Footing for Cantilever Retaining Wall

[DRLEI]

Have a topic regarding a Cantilever "L " Retaining Wall that is supported on a footing that is to be supported on Helical Pull Down Piles. Pile spacing in the front row (under the stem wall) is approx. 5 feet and about double that in the back row (at the heel). Height of retention is less than 5 feet and it serves at the end of driveways (mulitiple walls involved) into underbuilding garages on a man made island (earth fill and organice below hence the need for piles (buildings are on piles). Anyone have knowledge of a program (or other) that will design the footing for thickness to act sufficiently rigid to distribute loads to the piles and size the reinforcing for both the negative and positive bending zones between the piles. The footings (walls) are approximately 28 and 36 feet long (separate conditions based on site features and requirements).

 

[InDepth]

Think of it as a beam or slab supported by columns... Calculate it as simple spans.. And make your life easy, make the # of compression and tension helicals the same ...makes the contractors life easier

 

[DRLEI]

Thanks for the guidance InDepth. It was modelled as a plate (subsequent to the post) using STRUDL and the stem stiffness was not added to the plate. The pile guys do not
want to place more piles than are reasonably required. I spaced the back row on the retained side at about twice the front row spacing....works better that way for cost. At any rate, with all the reasearch I did, there was no program available at reasonable cost that could do the whole thing so it was done as efficiently as possible given the resources available.

 

[Ron]

Agree with InDepth for the most part; however, it is essentially a grade beam subject to torsion so I would probably approach the analysis more as a continuous beam and develop the moment at the supports.

 

[tbone73]

I agree with both InDepth and Ron. Space the piles the same for tension and compression. Also the beam or cap will be subjected to torsion and needs to be checked accordingly. In the long direction of the beam I would design it as a continuous beam also. In the short direction design the piles as cantilevered reactions bending the beam about the face of the wall.