The bottom course of facing panels are set and braced around the trestle.
Merchants Bridge, constructed in the late 1800’s, is the oldest rail structure crossing the Mississippi River, and is still used as a major route for freight. The bridge is currently being renovated to increase capacity and meet new engineering standards. Due to the high volume of freight traffic, it is a priority that the project optimizes construction schedule and minimizes track downtime. In the early stages of construction, The Reinforced Earth Company provided the contractor with a unique solution for renovating the bridge’s approach on the Missouri side. The solution used a modified MSE wall design that would allow for the existing trestle to be left in place so that the railroad could continue to operate during most of the construction.
The trestle volume was filled from the bottom-up with low-density cellular concrete (LDCC), enclosed by concrete panels, which were anchored to the fill with steel MSE soil reinforcements. MSE walls are typically constructed using granular backfill, however in this case the use of a conventional MSE wall would require more labor and time to compact the fill inside the volume around the existing trestle. The LDCC was flowable, required no compaction effort, and was placed in vertical lifts larger than a granular backfill would be. After the walls were constructed to the required grade, rail traffic was stopped, and new tracks were installed. The modified MSE walls with LDCC fill do not behave as a typical MSE wall, but on this project, it provided the needed benefit to the railroad’s schedule.