After the Flood: Plano-Coudon devises novel solution for Ellicott City retaining wall
The devastating aftermath of the 1,000-year rainstorm that struck Ellicott City on July 30th was easy enough to see, but in no way easy to fix.
The flash flood that swept down Main Street severely damaged dozens of buildings, as well as roadways, utilities and personal property. The six-inch downpour, which pushed the height of the Patapsco River up 14 feet in just 90 minutes, also compromised a vital piece of infrastructure – a stone retaining wall that separated the Tiber River from the B&O Railroad Museum.
Floodwaters had rushed up to and over the top of the wall, washing away part of the wall’s foundation, dislodging granite blocks and causing a 14-foot by 6-foot section of wall to crash down into the river below.
Without a strong retaining wall in place, “eventually you would lose all of that river bank and undermine the footings of the B&O Railroad Museum, so it’s an important wall,” said Blair Radney, Operations Manager for the Small Projects Division of Plano-Coudon Construction.
For weeks, Howard County officials searched unsuccessfully for a viable plan to restore the century-old structure. The project posed several acute logistical challenges. Crews would have to retrieve the huge stones from the river – a task that would ordinarily be completed by a crane. The tight, Ellicott City site included overhead power lines and communication cables which didn’t leave enough room for a crane to operate.
Plano-Coudon’s Radney began working to develop a process to rebuild the stone wall.
“When Blair proposed his solution, I just listened in wonder,” said Ryan Coudon, Co-Founder. “I just love this aspect of Plano-Coudon. We have knowledgeable, experienced people who can tackle very unique problems. I am proud that our company was able to address this very difficult situation. We were able to be a problem solver and an effective contractor to Howard County.”
Plano-Coudon’s solution revolved around unique and unconventional uses of equipment, some highly skilled tradesmen and meticulous coordination.
Rather than bringing in a crane, Plano-Coudon proposed parking an excavator on the roadway above the retaining wall and outfitting the excavator with special equipment which would enable it to hoist the fallen stones from the river. Workers needed to get into the river to rig up the stones to be lifted. But by temporarily damming part of the river, Plano-Coudon could ensure that work was performed in safe, shallow water.
Once they retrieved the stones and deposited them in a lay-down area, crews would still need to overcome several challenges to reconstruct the wall.
“Of course, there weren’t any photographs or drawings of what the wall looked like before it collapsed so we had to refer to the portion of the wall that was still standing to figure out how to fit the puzzle pieces back together,” Radney said.
A dry-stack construction, the retaining wall had held together for more than a century due to the careful placement of granite blocks, which got progressively smaller as they neared the top of the wall, and by the addition of deadmen – longer stones that extended back into the embankment and anchored the wall.
Expert masons were able to decipher the puzzle, but they also needed to gain physical access to the wall to guide the excavator in placing the stones.
“Setting up scaffold was an issue because you just can’t set up scaffold in a river,” Radney said. “Instead, we had to build the scaffolding from above the wall and use a suspended system, almost like a platform that you ride on rails down the wall, so that the masons could work with the equipment to put the stones back in place.
“Executing the project required detailed collaboration and communication with subcontractors and county officials. It also required paying careful attention to secondary issues, such as traffic. The excavator occupied a full lane of a roadway, requiring traffic management throughout the project. At the same time, the project in the heart of Ellicott City attracted many curious onlookers and necessitated practices to safeguard pedestrians.
The restoration, however, was completed in just two weeks in October.
“This was a very strange situation,” Radney said. “But we got the work done ahead of schedule and under budget, so the county was very happy.”