Columbia, the largest city in South Carolina, serves as the state capital and has a long history of offering picturesque charm. Keeping Columbia, named one of the “best places to retire” by CNN and other news organizations, beautiful is a main concern of its Public Works Department.
When part of its wastewater collection system needed fixing, the department looked to engineers at local consultant BP Barber, a part of URS Corp., to make the proper recommendations for repair. Severe deterioration and failure of a portion of the concrete sewer pipes installed in the early 1970s required that the city of Columbia take action to replace or rehabilitate this main collection and transmission line. The line serves a variety of areas—both commercial and residential—in the central and north Columbia metro area.
Consultants determined that a mix of solutions, including rehabilitating some of the existing pipelines with cured-in-place pipe (CIPP) and removing some of the existing pipes and replacing them with brand-new pipes, was required to fully restore the existing system.
The project was contracted in April 2010 with McClam & Associates Inc., Little Mountain, S.C., as the prime contractor. McClam & Associates performed the removal and replacement portion of the project, and Insituform Technologies Inc. performed the specialty CIPP rehabilitation.
Location represented one of the top concerns for the city and engineers: Much of the project was near a main traffic thoroughfare.
“I-126 is one of the main access points to the city for about one-third of commuter traffic,” said Bill Davis, wastewater engineer with the city. “It was absolutely necessary to not disrupt the flow of traffic in this area.
”Other sensitive areas included a 150-year-old Civil War graveyard and a monument in front of the South Carolina State Museum. Zero disruption to the Randolph Cemetery, listed on the National Register of Historic Places, was an absolute requirement. One portion of the pipeline ran under an interstate near the cemetery, with the manhole right in the middle of the interstate. Also significant was the fact that the wastewater lines ran parallel with the city’s source of drinking water, known as the Columbia Canal.
Davis described the first time he walked the right-of-way of the pipe in disrepair: “As I walked over the line, I realized that portions of it ran directly underneath gravesites that were nearly 100 years old,” he said. “It would have been completely detrimental to dig up this portion of the project.”
In addition to the complex job site, the 50-plus-year-old concrete pipe had deteriorated severely and required multiple-diameter transitions ranging from 48 to 54 in. depending on the depth and diameter of the pipelines. Whether dig-and-replace or CIPP was selected, the solution would have to fit within these requirements.
Ed Hart, senior project manager with BP Barber, explained how the consulting firm determined the solutions for each of the pipe sections: “While part of the project was in an undeveloped area, a portion of the project ran directly through downtown Columbia, with some pipes 25 ft beneath the ground,” he said. “We determined that a CIPP solution would be the most economical and cause the least disruption to citizens and traffic in these busy areas.”
An undeveloped area running along railroad tracks near the Congaree River was fixed using the remove-and-replace solution. The pipes in this area were suited for the replacement solution because they were shallow, and minimal damage would be done to the existing aboveground infrastructure.
The entire project consisted of 3,700 ft of remove-and-replace and 7,400 ft of CIPP rehabilitation.
Encompassing four separate installations, each of the shots had roughly 12- to 15-ft falls and was installed using the traditional water-inversion, water-cure method. The crew implemented bypass pumping (30 million gal per day) to accommodate for peak flow conditions while the CIPP was installed.
The upper half of the existing reinforced concrete pipe had deteriorated severely. Between 1 and 3 in. of the pipe wall was missing in some sections of the pipe, increasing the inside diameter from standard dimensions. This meant that in many sections the outside diameter of the CIPP tube was closer to 57 to 59 in. for the standard 54-in. concrete pipe. Comparably, the outside diameter of the CIPP tube for the 48-in. pipe averaged 49 to 51 in. Field measurements were taken for each section of pipe, and Insituform custom-manufactured the liner tube to allow for the increase in the inside diameter.
Engineers also addressed the issue of a 37-ft-deep manhole in the middle of I-126 that was to be abandoned. A 30-mm CIPP was installed through the manhole that transitioned from 48 to 54 in. during the 219-ft installation shot. Epoxy-coated rebars then were installed 6 in. above the top of the CIPP to provide added reinforcement and protect the installed liner. Subsequently, a concrete cap was installed to fill the abandoned manhole.
CIPP work began in April 2011, and the project was completed in June 2011. Insituform has a long history installing CIPP in Columbia, having completed more than 80,000 ft of CIPP rehabilitation in the city over the past five years.