Drilled pier with compressible foam in pier tip?

[dirtwoman]

I am the geotech for a project with a retaining wall that will be supported by drilled piers. The fine-grained soil gets stiffer with depth. The maximum depth of the drilled pier is 6 feet and the maximum wall height is almost 8 feet. This is a redesign of a retaining wall with a keyway. Currently, the wall is vertical above the grade. Below grade, the wall has a "shallow" foundation that varies in width to a maximum of 7.5 feet. The 2 foot diameter drilled pier is connected to the uphill side of the wall, 2 inches from the footing edge. The strucutral engineer designed the wall using the coefficient of friction along the "shallow" portion of the foundation. Because the soil becomes stiffer with depth, I am concerned that the friction along the "shallow" portion would not always be available. The structural proposes to use about 6 inches of compressible foam material in the tip of the drilled pier so that the stiffer soil would not be engaged during loading. Is this a reasonable solution? Thanks for any help! This project is under time constraints. (as usual)

 

[dirtwoman]

I wanted to let you know that I decided to not allow the compressible foam in the tip base of the pier. The wall has been redesigned. Thanks for your input!