Albuquerque Uses Versatile Lining Process to Rehabilitate Small Diameter Sewer Pipes
Like many municipalities across America, the city of Albuquerque, NM, is experiencing the challenges associated with an aging underground infrastructure. Addressing these problems with an aggressive repair and prevention plan isn't easy, especially when it comes to sewer lines. Pipes often run under heavily traveled streets, private property, and buildings.
When officials with Albuquerque's Public Works Department determined that a number of sewer lines had begun to show signs of corrosion, engineers investigated a variety of "trenchless" technologies - ways to eliminate the threat of pipe failure without expensive and disruptive excavation. <%=company%>, submitted the low bid and was selected to undertake the project. Using the company's NuPipe process, the installation crew inserted a specially formulated folded polyvinyl chloride (PVC) liner into more than 20,000 ft of 8-, 10-, and 12-in. sewer pipe across the city, providing renewed structural integrity throughout the wastewater collection system.
The successful completion of this substantial project confirmed the viability of PVC lining in small-diameter applications. But one of the most valuable results of the project for Albuquerque's Wastewater Utility Division has been the proof that this technology has the versatility to overcome the unforeseen problem and challenges that extensive underground construction typically involves.
Out of Sight is Not Out of Mind
When inspections revealed sewer line corrosion in scattered locations across the city, the Public Works Department began to assess repair options. The small void seen in the concrete pipes not only indicated a weakened condition, but also suggested other potential problems. As wastewater levels in the pipes rises during the city's peak water consumption period during the day, and falls during the low water-use time in the middle of the night, soil is pulled into the pipe from the voids. Given enough time, this could cause sinkholes.
Albuquerque's Public Works managers operate with the philosophy that it is more expensive and disruptive to wait for an emergency to make repairs, and they conduct regular assessments of the city's infrastructure to stop problems before they happen. This is an especially critical process when it comes to sewer lines, because they are "out of sight" and usually don't generate citizen repair requests until it is too late.
The Public Works Department is committed to the use of high-quality rehabilitation technologies, but also puts a heavy emphasis on cost-effective and conservation of tax-payer dollars. Among the possible solutions, the process of excavating and replacing the pipes was eliminated almost immediately, primarily because of the expense associated with digging, and the inconvenience caused by the prolonged closure of major streets.
A number of trenchless processes don't require extensive excavation, but some of these are not appropriate for small-diameter lines, and their construction materials - ranging from polyethylene to PVC - offer varying strengths and life spans. The department solicited bids from qualified rehabilitation companies, and Insituform Technologies, Inc., based in the St. Louis, MO area, was awarded the project, as noted earlier.
The sewer line deterioration in Albuquerque was severe enough to require complete structural repairs that would support the entire soil load if necessary, the fold-and-formed PVC system was chosen as a cost-effective solution to meet these structural requirements. The fact that PVC is believed to be the material of choice in more than 80% of the new sewers being constructed today further justified the choice of a PVC product.
The NuPipe rehabilitation process begins with the transportation of a coiled spool of the folded liner to the job site in a mobile steam trailer. The tube is then heated on site and pulled through the host pipe at a controlled rate using hydraulic winch. Once the pipe is in place and heated to a satisfactory temperature, a rounding device is propelled through it progressively unfolding and expanding it tightly against the walls of the existing pipe. Any water standing in the host pipe is pushed out ahead of the rounding device as it advances.
The liner pipe is cooled under internal pressure to form a solid PVC wall within the old pipe. Where branch connections occur, the tube forms a distinctive dimple, which allows location of the connection. The connections are subsequently opened from inside the pipe by a remote-controlled cutter. Once installed, the new PVC provides a jointless, smooth-walled pipe-within-a-pipe structurally designed for a service life of more than 50 years.
"On-the-Run" Engineering
High-quality trenchless products are typically versatile, but extensive underground rehab projects also require a flexible crew. Though installation planning and scheduling assume ideal conditions, the installations themselves often require contractors to handle less-than-ideal circumstances.
One of the lines in the Albuquerque job, for example, contained a horizontal deflection of about five degrees. Deflections can lead to "kinking" in the liner, but installers applied minor procedural changes using their expertise to prevent any wrinkling.
Other challenges arose from city ordinances that put a limit on noise levels in residential areas, yet mandate that work on major roads continue 24-hours-a-day. Consequently the Public Works Department managers had to ensure the team could complete a high-quality job within those noise parameters and work in night time conditions.
Probably the most unusual aspect of the job was encountered in a manhole that served another larger line. The pipe to be rehabilitated passed through this manhole in a ductile iron "sleeve." The sleeve was two inches larger in diameter than the rest of the pipe, indicating that the original intention was likely to have the concrete pipe continue through the iron pipe. The 2-in. differential and the heat sink of the manhole shaft meant that installers would have to take extreme care during the rounding phase to avoid bursting the liner or failing to generate enough heat for processing. The installation crew modified the process to control expansion of the liner, and incorporated a heat sock to retain the heat.
While these unusual conditions required experienced planners and installers, the most challenging aspects of the Albuquerque job -- like most jobs - were the unforeseen problems that called for creative, on-the-spot engineering. When some residents, for example, failed to comply with Insituform's request to avoid using tap water for a three-hour period, their use of water prevented the formation of a dimple at the in service connection. Without the signature dimple, the robotic cutter operator cannot visually determine where the service connects in order to reopen it. The installation crew previously had experienced this type of problem and used precautionary actions to ensure the connections could be accurately made and located. These actions consisted of recording detailed measurements during the pre-installation videotaping, and analyzing the varying levels of condensation on the inner wall of the liner during the post-installation videotaping.
Yet another challenge arose when a boiler truck malfunctioned. Typically, the loss of pressure and heat means that the partially rounded liner has to be scrapped and the installation process repeated. The crew reacted quickly, and made adjustments that compensated for the loss. The pipe was properly formed, and the delay that restarting would have caused was avoided.
Upon completion, the project complied adequately with all specifications. The rehabilitation is sound and actually has improved flow since the smoothness of the new pipe's walls compensates for the slight reduction in diameter.
The benefits realized by the city go beyond the physical aspects of the project. It was a goal, for example, to keep total cost below the $1.6 million originally estimated for relining. The Insituform team completed the job for less than $900,000 (a 56% saving), and agreed to perform some additional rehabilitation work not included in the original bid.
This relining project began in January or 1997 and was scheduled for completion last December. The contractor crew completed the entire project - including the additional rehabilitation work - by early April of 1997.
As budget pressure increase, it is critical that municipalities remain committed to performing preventive maintenance on underground infrastructure. Technologies have emerged that eliminate the prohibitive expense and disruption of underground pipeline maintenance. And, as experienced contractors apply knowledge gained from more and more field experience, it is becoming possible to undertake aggressive rehabilitation programs in increasingly more cost-effective ways.