New Jersey Department of Transportation chooses precast over cast-in-place.
By Paul Heidt General Manager, Garden State Precast
Along the serene western bank of the Passaic River in northern New Jersey runs Route 21. This major feeder freeway serves tens of thousands of commuters heading in and out of New York City, Newark Liberty International Airport and I-95. So when the New Jersey Department of Transportation (NJDOT) decided to restructure the old roadway to improve traffic flow and safety, it encountered a major engineering challenge.
Part of the project included replacing the aging Newark brick combined sewer, which was installed circa 1920. A high water table combined with the expensive costs of sheeting and dewatering motivated Dominic Salsa, project engineer at J.H. Reid, the general contractor, to propose an alternative precast concrete solution – a first for the New Jersey Department of Transportation (NJDOT). Upon obtaining NJDOT’s approval, Salsa contacted Garden State Precast of Farmingdale, N.J., to help fulfill the challenging project requirements.
Rising to the challenge
After more than 200 hours of engineering work, the precast concrete manufacturer designed 15 structures including some unit weights approaching 250,000 pounds.
To support the work, major project requirements included flexible rubber seals for 84-inch prestressed pipe, doghouse units for redirecting existing sewers and reversible sewage flows.
“The sheer size of these units required careful planning and coordination,” said Bruce Jamison, project manager for Garden State Precast.
Units measuring 12 inches and 15 inches thick with 11-foot-9-inch base heights proposed serious production and shipping challenges. The large base height was a major factor due to the 100-inch outside diameter of the pipe. To add further complexity, the units needed to be installed directly alongside the Passaic River with their top surfaces buried 10 to 20 feet below ground level.
The precaster coordinated the efforts with various suppliers to propose a workable solution to J.H. Reid and the NJDOT. A.L. Patterson Inc. provided technical support in selecting a proper lifting system, which was crucial in ensuring safety and proper rigging of all units. A.L. Patterson fabricated a large insulated curing cover for the project that provided a cost-efficient method for steam curing the units.
Flexible cast-in seals measuring 84 and 66 inches in diameter met strict tolerance requirements, ensuring proper compression and a watertight seal.
The 11-man production team constructed approximately one unit per week. With some concrete pours in excess of 30 cubic yards, project tolerances were a concern. All riser sections were match-cast on top of the base section, providing a perfectly matched joint for both the four- and five-sided units. Each section underwent vigorous quality control inspections to ensure the tolerances were maintained.
The 15 structures were shipped to the job on heavy lowboy trailers.
Tackling the unexpected
Several last-minute changes due to site conditions were addressed during production. Some sewers and building foundations were located only by excavation since there were no complete records of existing utilities. Various revisions such as rerouting were coordinated through on-site inspection of existing conditions.
Garden State Precast’s on-site supervisor, who managed the offloading and installation of the units and helped facilitate workflow and communication during the precast operation, immediately recognized that the rerouting had caused a change in the job termination. This last-minute change required the installation of an additional unit, so the order was made, completed and delivered in a timely fashion. Had the job been cast-in-place concrete, much more time would have been required due to forming, setting and the continued stabilization of the 30-foot hole as well as creating safety issues.
Getting the job done – on time, on budget
Regardless of the many challenges the job posed, Garden State Precast was able to complete the work to the satisfaction of both J.H. Reid and NJDOT.
“Precasting was a logical solution for a project of this magnitude,” said Salsa. “By choosing precast over cast-in-place, we were able to get the job done more quickly and efficiently and under much safer conditions.”
Each unit was installed in only two days – quite a contrast to a minimum 12 to 15 days for a cast-in-place unit. This, combined with enhanced worker safety, heralded precast concrete as an ideal solution to the sewer replacement problem.