CIPP liner selected as best method to rehabilitate water main
Installation of CIPP liner for Reversing Falls Bridge water main rehabilitation project proves to be an economical solution
The Reversing Falls Bridge traverses the Saint John River in New Brunswick and is one of only two bridges connecting the east and west sides of the City of Saint John. The Saint John Water Utility operates a 484 mm diameter welded steel water main suspended beneath the bridge which provides potable water from the east side to some consumers on the west. Due to recent issues with the pipeline and the need to rely on this critical pipe for many more years into the future, it was originally planned to replace this pipe. After extensive research, it was decided to rehabilitate the existing water transmission main by means of a fully structural cured-in-place pipe (CIPP) liner.
In late 2010, the water main beneath the bridge was taken out of service due to a leak at the bridge abutment on the west side of the Saint John River. Although the bridge is situated in the centre of the City, the New Brunswick Department of Transportation and Infrastructure (NBDTI) owns and maintains the structure. NBDTI wanted the leak fixed prior to putting the water main back in service. CBCL Limited was retained for engineering services to evaluate alternatives to repair or replace the leaking pipe. The exact location of the leak could not be determined, however it was known to be within the inaccessible piping that penetrated through the bridge abutment.
A variety of options were considered for the repair of the water main such as: spray-on liners, slip-lining, spot repairs (e.g. internal repair sleeves) and CIPP liners. The project has added complexity because of the size and location of the water main as most trenchless technologies are carried out on buried infrastructure. A major constraint for the project was to ensure that the repaired pipe would not impose any additional weight to the bridge structure. CBCL Limited determined that the construction of a new pipeline (including the temporary works required during construction) would necessitate structural upgrades to the bridge members in the $500,000 to $800,000 range.
Some of the key considerations for the project are summarized as follows:
- Weight neutral solution was required to satisfy NBDTI.
- Non-standard size of steel host pipe (484 mm O.D.) with circumferential and longitudinal welds and the potential to be out-of-round.
- Consideration of bituminous lining present inside host pipe.
- Consideration of expansion/ contraction of host pipe, fittings and bridge structure.
- Consideration of lateral bridge movement.
- Requirement to work around pipeline, multiple bends and reducers cast into concrete abutments which could not be accessed or modified.
- Hydraulic analysis required a minimal diameter reduction.
- Length between access pits at 220 metres (to span the entire bridge).
- Carrying out design and procurement around the schedule for the Harbour Bridge upgrades as NBDTI would not allow both bridges to be under construction simultaneously.
Upon consideration of the alternatives, the use of a fully structural CIPP liner was considered the most viable solution given the project constraints. The project was tendered and awarded to Galbraith Construction Ltd. with AquaReha b as their lining sub-contractor. The following is a summary of the project design and construction details:
- Weight neutral solution achieved by removing the bituminous liner and replacing with a CIPP liner.
- CIPP liner was able to navigate through four 11.25-degree bends cast in the bridge abutments.
- Expansion and contraction issues were mitigated with the use of a pre-liner to avoid bonding of liner to host pipe(allowing the liner and host pipe to move somewhat independently).
- CIPP liner was installed using the water inversion method over the entire 220-metre span.
- Construction was completed in four weeks as opposed to the 10-12 months projected for conventional pipe replacement.
- Construction cost was 26 percent of the estimate for conventional pipe replacement.
- Project risks were greatly reduced (not having to work beneath the bridge, shorter construction duration, minimal work in roadway, and lower overall construction cost).
- Social costs were minimized with shorter construction duration, one-way traffic maintained, and the pipe successfully returned to service sooner.
Several key factors led to the justification of this project, many of which are cost related. The construction of a new pipeline would prove to be significantly more expensive and require structural upgrades to the Reversing Falls Bridge. With the City of Saint John currently in need of major upgrades to its water system, economical solutions to enhance and prolong the life of infrastructure are needed. Rehabilitation of the existing steel water main by means of a CIPP liner has shown to be an effective solution at a greatly reduced cost when compared to conventional pipe replacement.