Water Environment Federation (WEF)

Trouble Shooting for Trenchless Liner Installation During Sewer Line Rehabilitation

- By: , , ,

Courtesy of Courtesy of Water Environment Federation (WEF)

Lining is being used by the utility industry as a cost effective solution to rehabilitate utility lines. Many types of liners, such as, cured-in-place-pipe (CIPP), fold and form PVC, deformed & reformed HDPE, etc., are being used to restore structural integrity of deteriorated pipes and to reduce inflow/infiltration. Most of the lining installation is carried out without any problem, however, sometimes installation does not proceed as expected and problems occur during and after installation. Occasionally it is necessary to rectify problems such as uncured soft liner from insufficient curing, bottom lift-up, ribs, pinholes, pokeholes, delamination, wrinkles, blockages due to liner shifting over openings, severed tie-ins at manhole locations, and non-advancement during inversions. This paper highlights several lining problems encountered in the field and offers trouble-shooting guidance. Experiences described herein include problems that occurred with CIPP and deformed & reformed HDPE liner installations. The review of these problems, remedial actions taken, and discussion of the lessons learned on the projects are intended to assist the engineer, owner, and contractor in taking appropriate actions to prevent potential problems and to correct problems on future projects. Field experiences from five (5) different lining projects are the basis of this paper.

Lining is widely used by the utility industry to rehabilitate deteriorated pipes, including sewer, water and gas lines. The lining industry provides a cost-effective solution to aging utility lines in the United States and other countries. The lining method is very effective in reducing inflow/infiltration (I/I) and restoring the structural integrity of deteriorated lines. There are a number of lining products and methods available in the market. The methods can broadly be categorized as CIPP, fold & form, deformed & reformed, and spiral-wound. Although all types of linings have been successfully installed in the field, occasionally problems occur during and after installation. This paper discusses some problems that were encountered, reasons that created the problems, and remedial actions taken on five different lining projects completed in Northern California. To protect the name of the project and the contractor, the projects are denoted as Projects A, B, C, D, and E. Lessons learned from all five projects are also presented.

Construction Sequence and Problems Encountered- Project A
Project A consisted of CIPP lining of 24-inch, 30-inch, and 84-inch storm sewer pipes. The contractor installed several segments of lining with no difficulty and then moved to the 24-inch lining. After all preparatory work was complete, the inversion of 24-inch lining started at about 12:30 p.m. on January 08, 2004. It was a wet day with low temperature (approximately 45 degrees) and rain showers. The pipe was flowing about ¼ full due to drainage from the yard of a commercial establishment. The ground was wet and moderate infiltration through cracks was noticed in CCTV inspection prior to inversion. The contractor elected not to use by-pass pumping because the flow was limited and the lining segment was only 80 feet. However, a standby pump was onsite to pump from upstream manhole as needed.

The inversion was quick and easy and 80 feet of 24-inch lining completed in 30 minutes. The inversion head was maintained at a level recommended by the felt tube manufacturer. Thermocouples set at the upstream and downstream ends measured the “cooking” temperature and determined when exotherm occured. The entire curing process lasted for 5 hours after which the liner ends were opened (at approximately 6:00 p.m.). Visual observation from the manhole showed a very soft and collapsed liner inside the host pipe. It was not possible to run the TV camera through the pipe due to the blockage from the uncured, soft liner. The infiltrating water was flowing heavily through the annular space between the liner and the host pipe and into the downstream manhole. When the uncured liner was inspected, another crew team was immediately contacted. The new crew came overnight with a higher capacity steamer and attempted to re-pressurize and re-cure the soft liner the next morning. Since both ends were open and no water inversion was possible, the ends of the liner were plugged with inflatable plugs before re-pressurizing the liner. This technique did not work well despite numerous attempts as the inflatable plugs were not able to sustain the 5 to 6 psi stream curing pressure. The new crew postponed the re-curing process on the second day at about 6:00 pm. On third day, the crew members were able to install suitable plugs on the ends of the liner and were able to “cook” the 2-day old soft liner for about 6 hours. When the cured liner was opened, visual observation showed an improved result; however, there was still liner lift-up at the invert in the middle of the pipe, as shown in Figure 1. The TV camera was able to proceed 30 feet from the manhole to the obstruction, but could not pass the obstruction. It was estimated that the lift-up, which was blocking 1/3 of the pipe opening but allowing the flow, was about 25 feet long in the 80-foot CIPP lining segment.

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