Lufti's project is in Florida because he's going to FDOT to pull permits on the sign. Pslem has a point though, hit the books and maybe the law will save you from doing anything about the sign altogether(except your lawyer's billable hours).
WePushPiles
Lufti, I agree the most economical would win, and since I don't know anything about the soils, sheet pile cofferdams might end up being more expensive than other methods. Dik makes a point about vibration issues if you are 5 or 6 feet from the sign, and you should consult your geotechnical...
GeoPaveTraffic, I'm glad you brought up the point of not being able to install pile on unstable embankments, and you're exactly right if you're using a conventional vibro hammer. The company I work for, however, can stabilize slopes using tubular sheet piles and have done it countless times in...