Large-Diameter, Non-Circular Trunk Sewer Rehabilitation Using GRP Composites

This paper reviews the preliminary design, detailed design and rehabilitation of two large diameter non-circular trunk sewers in Winnipeg Manitoba, Canada. The existing egg shaped, combined sewer trunks were constructed from brick and cast-in-place concrete with sizes of 2030 mm high x 1630 mm wide and 2980 mm high x 1980 mm wide, respectively. The original construction of the oldest pipe (the 2030 mm high egg) dates back to the 1880’s. Previous condition assessment programs highlighted significant deterioration of the pipelines including loss of invert in the concrete host pipe and reverse curvature at the crown in the brick sewer. Given their size and hydraulic significance, their rehabilitation was a high priority in the overall sewer condition upgrading program. A number of rehabilitation methods were considered as part of the preliminary design process, including segmental lining with glass reinforced polymer (GRP) composites, cured-in-place pipe (CIPP), spiral wound PVC, and bonded glass and carbon fibre reinforced polymer (FRP) systems. Each lining product/system was reviewed for its long term structural performance, constructability, quality assurance requirements, flow bypass requirements during installation, and the capital and life cycle costs of the rehabilitation. While a majority of the products reviewed had a long performance history, hand applied, bonded FRP liners are a relatively new concept and required considerable development of non-traditional rehabilitation design concepts. Bonded FRP’s have been deployed successfully in the water market in recent years on critical pipelines; however, the protocol to assess their viability for gravity sewer applications required development to facilitate consideration as an alternative to more traditional rehabilitation technologies. The introduction of multiple competitive alternatives for rehabilitation of pipelines of this size is complex and in this case delivered significant financial benefits to the owner. The paper reviews the preliminary and detailed design process, the procurement process used to assess equal but very different designs and the eventual implementation of the successful alternative, a segmental GRP liner, to deliver a new design life to these two critical sewer elements.