Flowable Fill (CDF) Under Retaining Wall Foundation

[DakotaKid01]

I am designing a spread footing retaining wall to replace a pile supported retaining wall. The wall is adjacent to the abutment wall of road underpass for a railroad bridge. The road is being realigned so they are removing the pile supported wall and putting a spread footing one in the same general area. It was suggested to use 2' flowable fill under the spread footing to provide a more solid base than the soil because there are worries about settlement of the soil under the current pile supported base because it hasn't been loaded. Settlement would be bad because the wall needs to stay aligned with the abutment wall of the bridge because there is a sidewalk. The current design is barely passing sliding and bearing checks. Is a CDF under the footing a good idea? Are there any other suggestions? Is potential settlement an issue? Thanks.

 

[cvg]

lots of questions that need to be answered.

[li]well, for starters what does your geotech say about it?[/li]
[li]have borings been done and has a settlement calculation been completed?[/li]
[li]will 2 feet of overexcavation eliminate settlement?[/li]
[li]will deepening the footing by 2 feet increase your allowable bearing strength?[/li]
[li]i dont believe this addresses your sliding problem[/li]

 

[BridgeEI]

I would think the friction coefficients between the footing and flowable fill would be lower than if it were soil. The flowable fill isn't very well cemented and you can create blemishes in the surface with your finger. At least the type they use in my area. I think sliding becomes a bigger issue then and you would need to add a shear key.

Will they be removing the existing piles? If so I can see settlement being an issue since you are disturbing all that soil when you extract them. If you are cutting them below grade and leaving them in place I can't imagine settlement being an issue unless you have poor soils.

If settlement is a concern, preload the site. Hopefully you have a geotechnical report that has some recommendations, if not I'd certainly get one done.