The U.S. Army Corps of Engineers, New York District, working closely with New Jersey Transit and contractors, placed an 850-ton concrete culvert underneath the Raritan Valley Line railroad embankment in central New Jersey this weekend as part of a major flood-risk management project.
Bound Brook Flooding
Communities in the Green Brook basin, including Middlesex Borough, have a long history of severe flooding. The United States Geological Survey notes the highest flood level in 200+ years occurred during Hurricane Floyd in 1999, inundating the business district and causing widespread loss of homes and infrastructure. Major floods have also occurred in 1971,1973, 1996 and 2011 when Hurricane Irene also caused record flooding.
Working around the clock, the entire project was completed between Friday evening and the early hours of Monday morning, allowing seamless commuter rail service to resume for 23,000 weekday riders on New Jersey Transit’s Raritan Valley Line.
Reducing Flood Risks
It was the first time in recent memory the New York District attempted an engineering feat of this magnitude. The project will reduce flood risks from Bound Brook, a stream running through Middlesex Borough. Placed next to an existing bridge culvert, it will provide an overflow during severe storms: When Bound Brook reaches a certain level, water will flow through the new culvert, reducing flood risk.
The culvert was built on site over several months’ time, curing for a minimum of 28 days (curing is a process where proper moisture, temperature and time allows the concrete to harden to the desired state.) Culverts function primarily as hydraulic conduits, conveying water from one side of a roadway/underpass to another. In this case, a railroad underpass.
Army Corps Project Manager Alek Petersen said: “Our team took on this engineering challenge because it provided the best flood-risk management option for the area. Our prime contractor brought in a sub-contractor specializing in heavy transport to ensure a successful outcome ─ which was exactly what we achieved.”
After the Friday evening rush and under the blaze of flood lights, workers began removing tracks atop the railroad embankment. Overnight the embankment was excavated down to competent shale ─ rock beneath surface soil and gravel ─ a process that lasted until mid-day Saturday.
Next, a gravel-like mixture of stones was laid several feet thick on top of the rock and compacted with heavy equipment. This material will support the culvert, embankment and trains passing over.
By 6:00 p.m., with steel plates laid as a guide, it was time to move the massive structure into place. Using a self-propelled modular transport system ─ a powerful apparatus with 250+ wheels capable of moving extremely heavy objects such as sections of bridge ─ lifted the 850-ton culvert several inches off the ground and began inching forward. Army Corps and contractor’ personnel carefully monitored the 45-minute maneuver until the culvert was placed into position within the embankment.
Saturday evening and into Sunday morning, the space around the culvert was filled with dense-grade aggregate (a mix of stone and stone dust) and compacted. Sunday afternoon, a gravel-like stone mixture (I-9) was placed atop the culvert to rebuild the embankment and provide a foundation for the ballast and rails. By 5:40 p.m. ─ nearly four hours ahead of schedule and 40 hours after work began ─ workers were putting the rail bed back in place. After several test trains successfully passed, the project was completed by 4:00 a.m. Monday. Full operation of the Raritan Valley Line resumed at 7:00 a.m.
The culvert works together with other levees, floodwalls and pump stations to function as an integrated system in reducing flood risk. The effort comprises one aspect of the larger Army Corps’ Green Brook Flood Risk Management Project. The Green Brook basin area encompasses 68 square miles, 13 municipalities and three counties in central New Jersey.