Like many historic districts, Old Town in Albuquerque, N.M., was struggling with its aging infrastructure. Hydrogen sulfide had eroded the reinforced concrete pipe, installed in the 1960s through the 1980s. When a sewer line collapsed, it often took a road with it.
After 10 years of using local construction firm AUI Inc. to repair the interceptors, the Albuquerque Bernalillo County Water Utility Authority took preventive action and hired Keith Reed, P.E., of Boyle Engineering Corp. in Albuquerque to design the renovation of 3,424 feet of 48-inch sewer line.
Capacity was a major concern, as the average flow is 11 mgd. The project also involved the Edith interceptor, which collects much of the city’s north central flows and runs one-quarter to half-full.
Because of the pipe’s weakened condition and lack of sufficient material for CIPP lining, Reed chose sliplining. “A 42-inch slipliner pipe would improve the interceptor’s capacity by 3 to 10 percent, but was inadequate to meet future needs,” he says. “A 44–inch pipe, however, would increase capacity by 11 to 19 percent.”
The increased flow is enabled by the smooth and efficient surfaces on the new pipe. Since 44-inch pipe is not an industry standard, city engineer Nancy Musinski, P.E., selected centrifugally cast fiberglass-reinforced polymer mortar pipe from HOBAS Pipe USA of Houston, Texas. The corrosion-resistant pipe comes in 2- to 3-inch increments. The installation was highly successful.
Fiberglass-reinforced
HOBAS pipe, a hybrid between concrete and traditional fiberglass, is made in 18- to 110-inch sizes in pressure and nonpressure classes. Sand (polymer) mortar in the core increases stiffness and strength, enabling pushes of almost a mile.
A flush bell and spigot configuration was chosen because the 44-inch I.D. replacement pipes have a 46-inch O.D., leaving more annular space for the insertion process. A gasket-seal system enabled contractors to install the 20-foot pipe segments live (sewer active), eliminating bypassing.
Sliplining is a semi-trenchless method. According to Kimberly Paggioli, P.E., vice president of marketing and quality control at HOBAS, generally successful reduc-tions have been a 5 percent diameter decrease between the host and liner pipe with minimum of 1-inch radial clearance.
AUI won the bid. “The most important aspect of sliplining is assessing the situation and what the existing pipe looks like,” says Mike Rocco, AUI’s trenchless division manager. “The more accurate the survey, the higher the success rate. Ignoring preparation is the biggest mistake contractors make.”
Rocco subcontracted Southwest Sewer Service Inc. in Los Lunas, N.M., to televise the lines, note the location of all service laterals, and identify which ones were in service. Those no longer in service were abandoned.
Working manhole to manhole, the AUI team cleaned the lines using a Vactor 2000 combination truck jetting at 50 gpm/2,000 psi. “We used a weighted interceptor sewer-cleaning nozzle with jet heads at the bottom so as not to spray the crown of the pipe,” says Rocco. “There was no tuberculation, just a severe case of corrosion.”
Using a Hitachi 450 excavator, the men then dug a dozen 25- by 12-foot entry trenches 12 to 18 feet deep at manholes and in other areas. All were shored using steel trench boxes with 3-inch walls. To remove the crown, they scored the pipe slightly above its springline, then cut using a target saw with a blade designed to slice through concrete and steel.
One, two, three — heave!
Before attempting the first sliplining run of 180 feet, Rocco mandreled a proof, dragging one pipe segment through the line to test the fit. “In these large-diameter interceptors, it’s easy to miss a little offset or point repair,” he says.
Pipes arrived with factory-installed hydrogen sulfide-resistant rubber gaskets under the bell ends. Workers slipped on the rear gasket before excavator operator Keith McClay lowered the pipe into the trench via straps. Using the bucket, he gently pushed this section into the bell sleeve of the preceding length.
AUI made a heavy metal push ring that fit precisely inside the bell of the flush joints to help distribute the force applied during the push. After McClay lowered it, men maneuvered the ring into position. Then the bucket jacked that segment into the sewer, and the process was repeated. The work was completed in one morning.
“Our shortest run was 80 feet, and the longest was 1,500 feet, but most averaged 600 feet,” says Rocco. “Preparation and backfilling both took two days, and we finished the project in two months.” However, a different 48-inch, 800-foot interceptor collapsed during that time, and Musinski told Rocco to slipline it, too.
In one place, the host pipe curved slightly toward the shaft, instantly halting the jacking process. “It looked straight on the inspection video,” says Rocco, who dug another entry pit and used shorter segments of pipe to navigate the gentle curve.
AUI subcontracted Condeck Corp. in Albuquerque to fill the annular spaces with Elastizell EF cementitious grout from Elastizell Corp. of America. The grout’s low density and high flowability reduced filling pressures.
Sliplining saved the utility 40 percent compared with open cut. AUI will return this summer to slipline more than 10,000 feet of interceptor sewer lines.
