Evanston Intercepting Sewer Rehabilitation
Metropolitan Water Reclamation District of Greater Chicago
Kenny Construction, Northbrook, Ill.
HOBAS centrifugally cast, fiberglass reinforced, polymer mortar, 110-inch-diameter pipe is used to slipline a 7,000-foot-long section of a deteriorating combined sewer system.
The Metropolitan Water Reclamation District of Greater Chicago (MWRD) is a regional wastewater agency responsible for serving an area of about 875 square miles in Cook County, Ill. The district collects, treats, and disposes the wastewater from 168 independently owned and operated local sewer systems. MWRD owns and operates approximately 535 miles of intercepting sewers as large as 27 feet in diameter. The present worth of the intercepting sewer system is estimated to be more than $4 billion.
The district has developed a program for inspection and preventive maintenance of the aging, intercepting sewer system to increase its reliability. The inspection program, designed to determine maintenance and rehabilitation needs, comprises physical inspection of manholes and sewer routes, closed-circuit television inspection to evaluate the inside condition of the pipe, and infrared inspection to locate cavities and voids.
Evanston, Ill., part of Chicago’s affluent North Shore region and home to Northwestern University, is directly north of the windy city and shares many common attributes, including its Lake Michigan waterfront. It was also the site of the longest, large-diameter sliplining project on record for the MWRD.
|Twenty-foot, gasket-sealed HOBAS CCFRPM pipe sections helped keep sliplining shafts small.|
Bid documents for the project included various options: segmental sliplining, cured in place (CIPP) lining, and insertion of panels. Kenny Construction of Northbrook, Ill., submitted a winning bid to slipline the sewer with HOBAS centrifugally cast, fiberglass reinforced, polymer mortar (CCFRPM) pipe. Jack Callahan, vice president of the underground group with Kenny, said, "We thought it would be the most economical option due to timing and the size. We do a lot of CIPP, but this was a little too large for that method considering the water situation, the bypass pumping that would have been required, and everything else. It would have been more difficult and expensive."
Paintal offered insight into the design process. "The design of the sewer lining was based on several conditions and parameters," he said. "The existing sewer was considered to be in a fully deteriorated state. Loading due to overburden and hydrostatic conditions was evaluated, and the liner needed the ability to withstand the corrosive environment."
Rehabilitation projects have many goals: reestablishing the structural integrity of the pipe, preventing leaking joints, and providing a corrosion-resistant liner—all while maintaining flow. "Capacity preservation is often critical on rehabilitation projects, and thin-walled HOBAS CCFRPM pipe very often provides increased flow capacity because of its superior hydraulics compared to the existing sewer. Even a downsize in diameter can easily be offset by the flow factors," said Kimberly Paggioli, P.E., HOBAS marketing manager.
|The pipe’s high compressive strength allowed long installation pushes.|
As with many projects, there were challenges to overcome, including the size and alignment of the sewer. "We have a lot of experience in rehab and have tackled some pretty tough projects," said Tom Gillis, project superintendent with Kenny. "Sliplining pipe of this size is not like sliplining with smaller sizes. This was an uncommon project, the first time it was done. The project went well and we made good production putting the pipe in. The slipline method of installation with HOBAS pipe is really a pretty slick operation."
This job is the largest-diameter slipline of this length of which HOBAS has a record. Prior to this one, there were two, 110-inch-diameter slipline jobs in Milwaukee. One sliplined 1,000 feet and the other 2,000 feet, but Evanston appears to be a record.
The sewer line under contract had a semi-elliptical cross section of approximately 10 feet by 10 feet. Kenny bid the project planning to rehabilitate all 7,000 feet with 110-inch-diameter pipe. However, upon closer analysis of the existing sewer, the company found that a reduction in liner diameter in several locations was necessary because the existing sewer was not round or straight and had many old repairs. Most of the sliplining pipe was in the standard HOBAS 20-foot length, but a small number of 10-foot sections were supplied where necessary.
"The first 2,000 feet of sliplining had been completed using HOBAS 110-inch flush reline pipe, which has an outside diameter (O.D.) of 114 inches," said Gillis. "Conditions we discovered when the job was started prompted a revaluation of the original design and resulted in the installation of 104-inch HOBAS pipe with an O.D. of 108 inches to be used for the remainder of the rehabilitation work,"
|Pipes were quickly joined and pushed while the flow was maintained.|
Most sliplining projects are located in congested areas with limited access to the line. In this case, pipe storage with immediate access was not possible. Metro provided a staging area about 1.5 miles from the site where 2,000 feet of 110-inch-diameter sliplining pipe could be stored. It was shipped from the HOBAS factory in Houston to the staging area, and then Kenny trucked it to the pit as needed. "We opted to get the first run of pipe on the ground before we started," said Gillis.
HOBAS customer service assisted Kenny in coordinating deliveries during installation. Gillis said, "We had a lot of conversations with the HOBAS shipping department. Rick Turkopp, HOBAS vice president of engineering, and the salesman came out several times. They were all very helpful."
"Initially we thought we would need three installation shafts, but we were able to do this with just two shafts because the pushing went so easily with the HOBAS pipe," said Callahan. "Access to the sewer was limited because of the 5- to 26-foot cover depth under the existing infrastructure, including roads and a railway."
The installation lines were quite long for pipe of such large diameter, so the pushing force required to install the pipe could be high if the friction wasn’t controlled. To decrease the friction, the pipe must be kept as neutrally buoyant as possible.
"The only issue with installing was to control the water to the level that would make the pipe neutrally buoyant," Gillis said. "Once we figured that out, we had no problem. Typically, we had 15 to 18 inches of flow, and we calculated that including the weight of the pipe, its contents, and everything else, we needed 27 inches of water outside the sliplining pipe to make it neutrally buoyant. We made some modifications and the pipe stayed buoyant."
Kenny Construction worked to find the best option for the grouting, which included several grout lifts in stages to prevent uplift. "The grouting wasn’t as simple as it would be on smaller-diameter projects since surface access was limited. Because this is an interceptor that is sensitive to rain, if you have a 6- or 7-foot bulkhead in the sewer and rain comes, that sewer is ineffective," said Gillis.
Although the grouting took some critical thinking, the pipe has high stiffness and has been performing well.
This article was contributed by HOBAS Pipe USA.