Abstract Manager

The Hull Causeway, part of the Chaudière Crossing that connects Ottawa, Ontario, to Gatineau, Québec, was widened to better accommodate active transportation. The existing bridge carried two lanes of traffic and a pedestrian walkway but lacked dedicated cyclist facilities. This forced cyclists to either share the roadway with vehicles or use the pedestrian walkway, creating potential safety hazards. The original design concept proposed widening the bridge by 1.60 metres to include a northbound cyclist lane while also constructing a separate prefabricated cycling bridge for southbound cyclists. However, this design faced significant challenges, particularly due to conflicts with a complex geological karst feature known as the Devil’s Hole.

This paper will explore the optimization of the superstructure to accommodate two 3.5-metre vehicular lanes, two 2.0-metre raised cycle tracks, and a 2.0-metre sidewalk, thereby eliminating the need for a separate cycling bridge. The innovative design effectively addressed the challenges posed by the Devil’s Hole. The original design required a costly and complex caisson foundation extending approximately 50 metres below the north abutment to mitigate the risk associated with the Devil’s Hole. Instead, an innovative alternative was developed: a reinforced concrete extension to the existing north abutment, constructed as a concrete pillar embedded in a rock pocket and tied to the bedrock and existing abutment with prestressed rock anchors and passive reinforcement dowels. This solution simplified construction, reduced costs, and provided enhanced structural stability.

The project also required the addition of a new steel plate girder, widening of abutments, and the introduction of a new approach span and associated substructure and foundation. Similar innovative interventions were applied to the new north approach abutment and the existing northwest pier foundation, ensuring the stability of the rock mass at the structure foundations.