Spanning the Mississippi River, Merchant’s Bridge is renovated and brought up to engineering standards using precast concrete and a licensed mechanically stabilized earth wall.
By Bridget McCrea
Merchants Bridge in St. Louis, Mo., is the oldest rail structure that crosses the Mississippi River. Built in the late-1800s, it is still going strong despite its age. Precast concrete is helping to extend its life after filling an important function in the bridge’s most recent renovation.
Last year, the Terminal Railroad Association of St. Louis (TRRA) enlisted the St. Louis Bridge Construction Company and Schrimpf Landscaping to help increase the bridge’s capacity and meet new engineering standards.
Working with The Reinforced Earth Company, Champion Precast built a solution that was used to renovate the bridge’s west approach on the Missouri side. Using a modified mechanically stabilized earth (MSE) wall design, the precaster made a wall that would allow the existing trestle to be left in place – a feature that ensured the railroad would continue operation during most of construction.
Steve Perotti, plant manager at Champion Precast, said the company works often with RECo, from which it licenses its MSE walls.
The project is broken up into two phases with the first phase encompassing nearly 60,000 square feet. Perotti noted the second phase, which is on the Illinois side of the river, will begin soon.
For the first phase of the project, RECo supplied Champion Precast with the molds and the shop drawings.
“We basically just took off with those plans and started pouring; it was a pretty straightforward project for us,” Perotti explained.
According to RECo, the trestle volume was filled from the bottom up with low-density cellular concrete (LDCC) and enclosed by concrete panels, which were anchored to the fill with galvanized steel MSE soil reinforcements. The LDCC was flowable, required no compaction effort, and was placed in vertical lifts larger than a granular backfill would be.
Once the walls were constructed to the required grade, rail traffic was stopped and the new ballast and tracks were installed.
Meeting close tolerances
Champion Precast did have to coordinate with Schrimpf Landscaping on load deliveries, use special headers for reinforcement and meet close tolerances.
“There was no coping to cover the top panels so those panels had to be made exactly to the shop drawing specifications,” Perotti explained.
According to Perotti, RECo handled all of the wall engineering, developed the shop drawings and provided the molds. He says the project worked out well, and he expects the same outcome for Phase II of the project.
“There’s another 50,000-or-so square feet on the other side of the river to do and it will all be done using the same MSE walls, which are working out really well,” Perotti said.
Bridget McCrea is a freelance writer who covers manufacturing, industry and technology. She is a winner of the Florida Magazine Association’s Gold Award for best trade-technical feature statewide.