Every sewer line repair job contains an element of the unknown. Because work is done below ground, surprises inevitably occur once the site is accessed—and some surprises are bigger than others.
In New Jersey, the Middlesex County Utilities Authority (MCUA) found more than they bargained for when they began repairing part of a 2200-foot-long sewer pipeline in February 2004. Originally installed in the 1950s, it serves as a critical link in the county's trunk sewer system. Two-thirds of the pipe had deteriorated from microbiologically induced corrosion, discovered during routine maintenance.
Located 20 feet below ground, the 7-foot-diameter concrete pipe had only three manholes for entry and exit; two of these were installed as part of the contract to make access to the work area safer. In addition, the work was to take place in the middle of winter, so the restoration materials and environment had to be heated. This wasn't easy, given the remote location of the line—manholes providing access were approximately 1½ miles from the nearest road. Also, because the sewer runs parallel with the Raritan River, the jobsite could have flooded during high tide.
Jacobs-BBL, Piscataway, N.J., served as project engineer for the MCUA. Engineers explored a variety of repair solutions. Complete replacement was deemed too costly and unrealistic, given the layout. The project's principals also determined that pipejacking or sliplining would be inconvenient, expensive, or both. Jacobs-BBL found that Pittsburgh-based Sauereisen's Underlayment No. F-120 gunite formulation would be most efficient because it would enable the pipe to be repaired from the inside, without excavation. The fast-setting resurfacing material with high early strength comes is designed to be used with a corrosion-resistant topcoat, such as an epoxy, and can be topcoated as early as five hours after application.
However, after fully exploring the site, project general contractor Swerp Inc., Lafayette Hill, Pa., discovered the damage was much more extensive than originally thought. Swerp informed Jacobs-BBL and the MCUA that a thicker application of resurfacing material would be required to adequately repair the damage. Swerp originally had planned on using a small concrete pump in the pipe to apply the material, but later determined expediting the project would require a different machine and formulation.
Swerp enlisted subcontractor East Coast Gunite of West Orange, N.J., because of their expertise in applying similar products. The contractor installed the anchors, placed reinforcing wire where necessary, and gunited the underlayment to a thickness of up to 4 inches prior to finishing the material by hand. This stage of application effectively restored the pipeline's integrity.
The underlayment application took approximately three weeks, requiring 6300 bags—roughly 315,000 pounds—of the product. Because of the location of the damage, workers had to apply the product overhead (the greatest concentration of municipal wastewater corrosion typically occurs above the water level). Swerp followed up by spraying on Sauereisen SewerGard 210, an epoxy polymer lining, to prevent recurrence of microbiologically induced corrosion.
The underlayment provided a high-quality, economical solution. “Using this method of restoration versus pipejacking or sliplining saved 20% to 30% in costs for the county,” said Jacobs.
— Lauren Bossers is a Pittsburgh-based business writer.