The CSX Florence project team faced a tough challenge at the outset. How to replace a double main line freight train bridge if the trains can’t be delayed during construction? In partnership with the owner, CSX, and our design partner, Bergmann, the team answered this question with accelerated bridge construction techniques, a set of practices that help reduce construction schedules while improving safety and quality.  

The first was the design of a new superstructure that mixed prefabricated and cast-in-place materials. It included cast-in-place pier caps and drilled shaft foundations supporting six steel girder spans, 34 pre-cast deck panels, and six pre-cast walls. The pier caps were made wider than usual, which allowed the excavation and installation of the shaft foundations with no stoppage of trains.

With the new substructure in place, the next step was to remove and replace the existing bridge. The team divided the two-line bridge into six sections—three for each set of tracks on the bridge. Each section was replaced in a separate six-hour window, during which all rail traffic was shifted to the other line.

Each section was cut away and lifted out by a crane, using pre-installed rigging to save time and increase efficiencies. The prefabricated steel girders and pre-cast deck panels were then installed on top of the cast-in-place substructure. 

Spans were replaced every other day to give the team time to stage the prefabricated materials for installation and remove the old sections of bridge from the job site. After two weeks, all six sections of track had been replaced.

With creativity, careful teamwork and abundant communication, the CSX Florence team utilized the latest accelerated bridge techniques to deliver a seamless replacement of this critical piece of infrastructure.

The trains never had to stop rolling, just as the client wanted.