Foundation Design for Crowchild Trail Short-Term Improvements

Crowchild Trail is a major arterial road in Calgary. Originally constructed in 1967, the crossing of the Bow River had become a cause of major traffic congestion. As part of the short-term improvements to Crowchild Trail, a road and bridge widening program was proposed to add additional northbound and southbound through lanes and reconfigure the on-ramps to the northbound lanes to relieve congestion. This presented three main geotechnical challenges: (1) insufficient factor-of-safety on the eastern slope of the south approach fill, (2) the potential of differential settlement between the existing abutment and the connected abutment extension, and (3) the ability to reuse the in-river bridge piers. The original construction of the south abutment used a spread footing on a large earth embankment. To facilitate the addition of one new northbound lane and two on-ramps, an abutment extension was required. This necessitated the construction of additional fill on the side of the existing steep abutment slopes. Due to the proximity of existing roads, the new lanes would need to be supported by a multi-tiered retaining wall. The foundation soils were not suitable to allow the construction of a multi-tiered MSE wall; therefore the bottom tier was designed as a spaced anchored pile wall. An additional complication was the need to connect the new abutment to the existing abutment. The abutment connection needed to be made before the addition of the majority of the load, which consisted of bridge girders and decking. This presented the potential to crack the abutment if too much differential settlement occurred. It was initially proposed to place the abutment extension on piles; however, this had the potential of creating a stiffness imbalance under cyclic traffic loading, which could also result in cracks developing along the abutment connection. Ultimately, a load transfer platform was designed to support the abutment extension and match stiffness between the new and existing fills. This paper describes the geotechnical considerations that went into developing the design and evaluating the ability to re-use the in-river bridge piers. The paper also presents the design and performance of the anchored pile wall and abutment extension, which used 2D and 3D numerical modeling techniques. The performance of the anchored pile wall has been monitored during service, which shows the seasonal effects on anchor loading that are also presented within the paper.