In New York City, the title of "The Interceptor" might bring up visions of an all-league defender who steals passes for one of the city's professional sports franchises. To see the real interceptor in action, city residents would have to go where they don't want to go, to see what they don't want to see. They would have to open a large sewer manhole near the South Street Seaport and clamber 30 ft. down a shaft with the sound of sewers bubbling.
NYC DDC photo
New York City's interceptor does not wear a sparkling uniform; instead, the interceptor is a vault-like concrete box that intercepts sewers from around the city and channels the sewer safely into the municipal water treatment facility.
Recently, the city's star interceptor was close to being benched. The concrete chamber's walls were crumbling and badly in need of repair. Rain events and water gushing via cracks, fissures and gaping holes inside the sewer from the nearby East River compromised the tunnel and threatened partial sewer line collapse and overflows.
New York City Department of Design and Construction (DDC) took on the project, which became more complex as the DDC team and contractors studied the issue. The team was led by Iyad Marzouq, assistant commissioner of DDC's Infrastructure Division, and Bishoy Sourial, resident engineer. The contracting team was led by David Beesley of Coppola Services in Ringwood, N.J.
Many projects of this nature would use a "cut and cover" approach, which could include rerouting traffic for many weeks. This would give workers plenty of room to safely access the sewer with the appropriate machinery.
However, none of these normal steps were acceptable. The sewer is in a busy area where hordes of tourists walk to the South Street Seaport in the summer. Also, planners had inadequate space to relocate to nearby roads. In addition, large bridge supports for the Franklin D. Roosevelt East River Drive are located nearby. Relocating the multiple underground utilities from the tunnel also seemed impossible.
After months of strategy sessions, planning and researching, the team came up with an elegant solution. The strategy had not been used in a NYC sewer before and ended up costing only $29 million while completed in just under two years.
NYC DDC photo
The planning team, including NYC DEP, used a process that employed equipment that could create the equivalent of a PVC pipe inside the sewer, without moving utilities. The machinery also could do its magic without being deterred by water and without using chemicals.
"All of the traditional means of rehabilitating a sewer pipe were unsuitable for this project," said Marzouq.
Often used CIPP, cured-in-place-pipe lining, requires a completely dry working surface inside the sewer to work, which was not possible in these types of sewers. Slip lining (aka jack and bore) needed a jacking and receiving pits dug up 30 ft. deep on each side of the existing sewers, which also was not feasible. It also is designed to work for circular pipes, so it will result in 40 percent flow capacity loss if inserted inside this rectangular sewer. Shotcrete method, which sprays a special concrete mix around the inside of the sewer pipe, was tried and failed previously. New gushers and cracks continued to form as soon as work was done.
The design team discovered a method known as Spiral Wound Lining, offered by SEKISUI SPR as the answer to construction in such a confined space. Using this trenchless equipment and method saved time and kept inconvenience at a minimum for people in the city's financial district.
The equipment was lowered in pieces 30 ft. below street level through an existing sewer manhole. Workers then assembled the winding machine at the proper position. Motors, bearings and gears were calibrated so the equipment could rotate the SPR material around the circumference of the interceptor sewer. Project planners carefully set up the machine to ensure a safe environment for workers in the interceptor area.
Rerouting the Sewer Flow
NYC DDC photo
According to Mazouq, "The existing live sewer flow needed to be reduced considerably to allow for safe working space for the workers, so five large submersible pumps were utilized underwater to divert just enough flow inside the interceptor sewer upward through the manhole and under the street pavement to a neighboring combined sewer manhole 30 feet away via a combination of manifolds, risers, valve, pipes, and other fittings by-pass system."
"Many things were unusual about this project, including the need for fully equipped divers to install the submersible pumps at the start of the project," he added.
Workers could then begin using the Spiral Wound Lining equipment to begin building a liner through a continuous winding process. Workers were building a pipe inside a pipe. The machine installs the profile that is fed from a spool at the top of the manhole by winding it around the circumference of the existing pipe and interlocking the profile as it pushes forward in a zipper like mechanism.
The construction team used grout to fill the voids left between the existing sewer concrete wall and the new PVC lined wall. This process also increased the structural strength of the new sewer structure.
"Our construction team has fixed about 1,050 feet of pipe with reinforced PVC," said Marzouq. "This has all been accomplished without street closures and traffic detours. Traffic volumes were not affected, and the community did not feel much inconvenience."
Marzouq summarized the effect of his team's work on the 1960s-era interceptor.
"The potential risks of flooding have been reduced, and we have found an innovative way to extend the lifespan of the interceptor. I believe that with this project, DDC has found new means to efficiently maintain the city's infrastructure while keeping costs and disruptions to a minimum." CEG
