An abutment wall, with a maximum 30 ft. height, to the proposed grade has been suggested.
~ Proposal is to use temp tieback wall to excavate slope back to existing end bent, similar to Hillsborough St. bridge in Raleigh. Abutment wall would be MSE wall, possibly using a cast-in-place face. The MSE wall option would require a 2'-6" thick crash wall to be built in front of the MSE wall.
~ Straps for the MSE wall could be up to 35 ft. long.
~ Bridge would be supported on 2-tsf spread footing bearing on MSE wall fill. Spread footing avoids need to drive piles near historic building, and is cheaper than drilled piers.
~ MSE option may not be feasible. Alternate is to use a shaft wall.
~ Abutment wall – 30 ft. maximum height to proposed grade. Right side wingwall/retaining wall also 30 ft. in height. Shaft wall option inefficient and expensive due to 30 ft. height and 20 to 25 ft. depth to rock. Would also require lightweight aggregate.
~ Use of Geofoam fill behind the wall ruled out due to the complex geometry and cost.
~ The Department should consider options that eliminate the crash wall.
~ Other concerns include the effects of post-construction settlement.
