Depth to Fixity - Pile in MSEW

[Trouser]

I am working on a foundation for a bridge over the interstate that requires the use of pile foundations through MSE walls that are approximately 30 feet in height. The structural design engineer in our unit is concerned about how the unbraced length of the pile will effect the axial capacity of the pile section. How is this unbraced length determined? Is it related to the depth to fixiity?

Typical details that I have seen for this foundation type include isolating the piles from the MSEW by placing CMP around the piles and backfilling with a loose/low strength material such as pea gravel.

Should the pile be considered unbraced through the entire MSEW or can the pea gravel be used in a typical depth to fixity calculation such as the one outlined in AASHTO LRFD 10.7.3.13.4?

 

[ron9876]

The geotech normally will provide this info.

 

[hokie66]

I would share the concerns of your structural design engineer. It would depend on how far back the piles are from the face of the reinforced earth wall. If close, I would consider the piles to be unbraced. Another concern would be the affect on the embankment stability caused by the piles disrupting the earth reinforcement.