The Town of New Tecumseth located approximately 90 km northwest of Toronto, owns, operates, and maintains both distribution and transmission watermains.
During a routine watermain inspection, town operations staff observed a large sink hole located beside an existing drain chamber. This drain chamber is part of a 400-mm diameter high-density polyethylene (HDPE) transmission main that runs in a north-south direction adjacent to Sir Frederick Banting Road. This existing pipe has four 45-degree bends as it crosses beneath the Boyne River.
Town staff completed a further inspection and determined that the drain chamber should be pumped out and a man-entry inspection should be completed. R.V. Anderson Associates Limited (RVA) was retained to assist the Town in locating the cause and determining the best solution available to repair the leak.
RVA completed a man-entry inspection into the drain chamber with the assistance from the Town. Active ground water was observed leaking through existing cracks in the concrete walls only. It was decided that we needed to investigate the watermain directly below the sink hole to see if there were any leaks that was causing water to flow out.
ASI Marine was contacted to undertake an internal camera inspection into the watermain to locate the source of the leak. This inspection was conducted using a flexible camera that was inserted through a 150-mm diameter drain valve, then pushed into the 400-mm HDPE pipe. The inspection was successful, as the leak was found in the HDPE portion of the watermain, at a butt fusion joint approximately 4.3-m from the south wall of the drain chamber, directly below the sinkhole.
To stop the leak, various repair methods were reviewed.
Open-Cut Repair Option
The open-cut method was reviewed but was rejected as the drain chamber was located approximately 20 m north of the Boyne River, where the groundwater levels in the vicinity of the repair are high. The open-cut repair option would require the installation of a temporary shoring and dewatering system to mitigate high groundwater levels and poor ground conditions. The repair would include the installation of a new repair coupling.
Internal Repair Sleeve Option
The second option evaluated involves the installation of an internal repair sleeve. This repair would require removing the existing 350-mm diameter gate valve and associated appurtenances within the drain chamber after the watermain was drained, then inserting a Link-Pipe Hydro Sleeve through both the 350-mm diameter DI pipe, down past the existing transition coupling into the 400 mm diameter HDPE watermain where the leak has been previously located.
The sleeve is constructed of an inner stainless-steel layer and an outer resilient layer which is ultimately compressed and cemented with an adhesive against the inner wall of the host pipe. This repair sleeve is temporarily reduced in size to allow insertion through the smaller pipe and coupling, then enlarged into place by use of air pressure. Under normal circumstances, a contractor would pull this sleeve into place. However, there is only one access into the watermain through the drain chamber, therefore this sleeve would need to be pushed into place using pushing rods through the existing 350-mm diameter ductile iron pipe, then through the transition coupling into the 400-mm diameter HDPE pipe to the leak which is approximately 4.35 m from the south valve chamber wall.
Prior to installing this sleeve, the 350-mm diameter gate valve in the drain chamber would need to be removed and the watermain flushed to remove any accumulated debris that may have washed into the pipe from the leak.
A CCTV camera inspection would then need to be completed to obtain an accurate measurement for the actual leak location to ensure that the sleeve can be pushed down the pipe to be centered over the leak. The CCTV camera and tether would need to be completely disinfected prior to this inspection.
After the Link-Pipe Hydro Sleeve is pushed into the place in the clean pipe, it is expanded into place with pressurized air and a ratcheting locking mechanism on the stainless-steel section of the seal. An adhesive applied on the exterior of the sleeve is then allowed approximately 24 hours to cure. Unfortunately, this repair system was not NSF61 approved at the time of this project.
Watermain Lining Using Primus Line
Primus Line, manufactured in Germany, is the only trenchless lining product available that can be used to line an HDPE watermain, is NSF61 approved, and does not require any curing.
Primus Line is a flexible hose capable of going through 45-degree bends as it is pulled into a watermain through an open section of pipe. Air pressure is used to inflate this liner against the HDPE pipe wall, then is replaced with water. For this liner to be installed, a temporary access shaft would ne to be constructed.
To reduce the risk of a liner becoming stuck during pull, it was recommended that an internal CCTV watermain inspection be completed. The purpose of this inspection was to confirm the vertical alignment (bends) of the pipe as well as any reduction in the ovality of the HDPE pipe. In addition to this, the inspection will also confirm if there is any debris that could prevent the liner from becoming trapped.
A comprehensive product review and constructability analysis was completed to determine the best solution to repair this transmission main and get it back online, Primus Line was chosen as the best solution based on ease of installation and cost.
Tender drawings and specifications were prepared, and Pipeflo Contracting Corp., of Hamilton Ontario, was chosen to install this Primus liner. Pipeflo Contracting is a trained and approved installer for Primus Line.
To confirm that the liner would fit and be able to travel through the four 45-degree bends, a CCTV inspection was completed. CCTV inspections of water transmission mains are rare as most CCTV inspections are carried out in sewers. Per the detailed specifications, Pipeflo had to use a water camera which is only used in watermains. Pipeflo found a portable CCTV camera and completed the internal inspection. Pipeflo Contracting used a drogue parachute to string a line through the watermain. A polyline rope was used to pull the CCTV camera crawler up the pipe and through the four bends. Both the CCTV camera crawler and rope was disinfected prior to this inspection.
The inspection was successful as it was determined that the liner would fit properly and travel easily through the bends. Pipeflo ordered the liner from Primus Line in Germany and planned for delivery in Toronto. Due to the timing, the liner was flown from Germany rather than sent by container ship. In advance of receiving the liner, Pipeflo crews installed a temporary access shaft in an existing driveway entrance to the Town’s sewage treatment plant, approximately 100 m south of the drain chamber.
Approximately four weeks later, the liner along with the specialized connectors arrived in Toronto and were transported to New Tecumseth for installation. An experienced installation technician from Primus Line was sent from Germany to assist Pipeflo and provide on-site QA/QC as written in the technical specifications.
A tag line was installed in the watermain from the temporary access shaft to the drain chamber. This poly line was used to pull the CCTV camera through the watermain after a final watermain cleaning was completed.
The Primus liner – which came on a large wooden reel – was set-up beside the temporary access shaft and was connected to the poly tag line. Pipeflo crews were set up at both ends and began the process of winching the new Primus liner from the temporary access shaft through the HDPE watermain to the drain chamber.
Air was used to inflate the liner and the specialized connectors were installed to hold the liner in place both at the drain chamber and the HDPE pipe at the temporary access shaft. Pipeflo crews re-connected the watermain in the access shaft to the existing PVC water and reconnected the valve and associated appurtenances within the drain chamber.
The watermain was filled, pressure tested and disinfected and finally put back into operation. All told, the construction took approximately a week, considerably less than an open-cut approach to repair the watermain.
David Crowder, C.E.T., is the trenchless practice leader for R.V. Anderson Associates Limited. Rob Greenwood, PMP, C. Tech, is a project manager for the Town of New Tecumseth.