Design and Construction of a Four Span Rail Bridge as Part of the Waverley Underpass Project

The Waverley Street Underpass Structure is a four-span (18m-18m-22.5m-18m) simply-supported rail bridge that carries both the north and south Canadian National Railway (CNR) mainline over Waverley Street (Waverley) in Winnipeg, Manitoba. The Underpass replaces an at-grade crossing where over forty trains cross a day along with 30,000 vehicles, which is a safety concern and caused traffic congestion and delays. The underpass will accommodate four northbound lanes and two south bound lanes as well as an active-transportation (AT) pathway on both sides of Waverley.  The bridge superstructure consists of ten lines of steel plate girders cast into a reinforced concrete deck at a skew of approximately eleven degrees to the substructures. The girders are designed as the primary members to satisfy the Ultimate Limit State while the composite section, comprised of steel plate girders and concrete infill, is considered only to satisfy Service Limit State requirements. The abutments are founded on sixteen H-piles while the three piers are founded on three rock-socketed caissons per pier designed with rock socket lengths of 4500mm for exterior caissons and 5000mm for the central caisson at each pier. The structure was generally constructed at grade with the bulk underpass excavation occurring after the bridge completion. A rail shoofly ensured uninterrupted rail service during construction. Two significant challenges encountered during the construction of the rail bridge were unexpected geotechnical conditions and quality control/assurance during structural steel fabrication. Unexpected subsurface conditions affected the installation of two rock-socketed caissons when a karst system was presumably encountered causing the depth of competent bedrock to be approximately 15 meters below the anticipated elevation found during the installation of the test caisson prior to the start of construction and found during installation of the other seven bridge caissons. The extended depth of the caissons necessitated a team effort for design changes and construction methodology changes to avoid schedule delays to complete the bridge, which could have been exacerbated if the window for completing rail works before winter was missed. The fabrication of the structural steel faced challenges with respect to material procurement and in some instances, quality of fabrication. Additionally, creative means and methods requiring modifications to the bridge structural steel works were required to form and pour the concrete superstructure. Despite the issues encountered, the bridgeworks were completed on schedule and the remainder of the underpass project remains on schedule for Substantial Completion to be achieved in September 2019.