Pushing the Envelope—Rehabilitation of Non-Circular Sewers Up to 2.7 m (9’) High with Reinforced Cured in Place Pipe

The city of Winnipeg, MB, Canada, has a large and old combined sewer network that was constructed using a wide range of materials, cross sections, and construction methods. As with many jurisdictions in North America, their rehabilitation needs have become considerably more challenging over time. This paper focusses on the design considerations to rehabilitate two sites with egg shaped monolithic concrete combined sewers with numerous major defects in the form of sewer fabric decay (i.e. general surficial material degradation), localized invert loss, infiltration, and longitudinal four point fractures. The sections included pipes that were 1,800 mm high×1,350 mm wide (72”×54”) and 2,700 mm high×1800 mm wide (108”×72”) and conveyed dry weather flows ranging from 1.9 to 162.8 L/s (30 to 2,580 USGPM), respectively. The combination of defects present with active infiltration meant that active deterioration processes were present in form ground loss around the sewers. The sites themselves posed considerable access challenges, as one was located on a former road right of way now leased to a private recycling company and located adjacent to active Canadian Pacific Railway (CPR) tracks. Proximity to active rail tracks necessitated seeking approval from CPR on a detailed sequential phasing plan for the shaft construction. Since the requirements for the shafts were dictated by both the rehabilitation method and the contractor’s means of shoring construction, final approval for shaft construction at the site could not take place until after contractor procurement. Design and procurement included five unique rehabilitation alternative systems: reinforced cured in place pipe (CIPP), grouted in place glass reinforced polymer (GRP) liners, bonded in place fibre reinforced polymer (FRP) liners, centrifugally cast concrete pipe (CCCP), and grouted-in-place spiral wound PVC strip liners. Each technology was assessed and specified based on their unique installation and long term performance characteristics. While all of the deteriorated pipes appeared stable and were not at risk of short term failure; some of the pipes displayed evidence of accelerating deterioration which required a rehabilitation system designed for full pipe-soil loading models as well as hydrostatic groundwater loads. Design methodologies and minimum quality assurance (QA) requirements were dictated by the tender documents for each rehabilitation technology to promote an “equal” assessment of alternative technologies in a competitive environment. The rehabilitation contract was awarded based on the use of reinforced CIPP technology in late 2017 and installation of the liners was completed in November 2018.