B&N was retained by the Jefferson County Engineer to replace the 108-foot-long, single-span steel truss bridge carrying the two-lane County Road (CR) 74 over Cross Creek and reconstruct approximately 800 feet of approach roadway. The replacement structure was built on a new alignment over Cross Creek to allow the existing bridge to remain in service during construction and maintain traffic through the project site. The roadway reconstruction was phased to minimize the amount of time the signalized, one-lane bi-directional maintenance of traffic solution had to be in place.
B&N’s alignment design allowed the replacement span to be shortened to 91 feet. A composite weathering steel beam superstructure was selected after determining that it would be too difficult to deliver prestressed concrete beams of that length due to the tight curves along all roadways leading to the project site. Steel fabricators also indicated that there could be issues delivering the beams, so a bolted field splice was included in the project plans to give contractors added flexibility.
Site constraints including bedrock depth, boulders, and the need to maintain traffic, required an innovative design solution for the bridge’s forward abutment. Soldier piles were placed in drilled shafts that were socketed into the bedrock. This eliminated difficult and expensive temporary shoring and minimized the amount of rock excavation required for construction. Additional “plug" shafts were constructed between the main drilled shafts that contained the soldier piles. This created a cofferdam and provided a solid base for the abutment. Low strength mortar was used as backfill behind the abutment to minimize lateral pressure on the wall and the resulting deflection of the soldier piles. This solution was more cost effective and easier to construct than using rock anchors to provide lateral resistance for the abutment wall.
A temporary construction access road crossing the creek was provided during construction due to the poor condition of the existing bridge and a load restriction on a nearby bridge. Plan details were created and right of way and a USACE permit were obtained to provide contractor access.