All,
Can some body suggest me some good references or info about "how to estimate surcharge (lateral pressure) from existing buildings and/or local traffic" that can be used for tie-back shoring wall design?
AASHTO LRFD bridge specification has some good info on traffic and other surcharge pressures but it would be hard to justify that purchase if this would be the only thing you need that code for. For traffic it's typically considered as a uniform pressure equivalent to an additional 2 feet of fill unless vehicles can drive perpendicularly right up to the edge of the retaining structure (then it varies between 2 - 4 ft if I recall). Often the vehicle surcharge is stopped at 8 feet below grade.
Also, here's a spreadsheet I developed for pressures on buried structures (originally intended for manholes with aircraft wheel load surcharges). I make no warranty that this is correct and all that legal disclaimer stuff (use at your own risk).
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries