Geotechnical Seismic Retrofit of the Knight Street Bridge in Metro Vancouver

The Knight Street Bridge, built in 1974 over the Fraser River, connects the City of Vancouver to the City of Richmond via Mitchell Island. The bridge was recently seismically upgraded. Liquefaction of Fraser River sand is the key issue that affects the seismic performance of the bridge. Seismic soil-structure interaction and deformation analyses were conducted to assess, design and optimize seismic retrofit measures. Geotechnical retrofit measures included ground densification schemes at three abutments and addition of steel pipe piles at a pier adjacent to the riverbank. Limited head room under the deck, existing underground utilities and proximity of the densification zones to the Fraser River posed challenges in selecting appropriate and cost-effective ground densification techniques. Compaction grouting was used for an abutment with very low headroom, and timber compaction piles were used for densification in other areas. A method specification, rather than the more conventional performance specification, was adopted for timber compaction piling. The seismic upgrade of the bridge was successfully completed in November 2011. This paper focuses on the key challenges faced in the design and construction of ground densifications and retrofit of the bridge.

Thavaraj, T. and A. Sy. 2013. “Geotechnical Seismic Retrofit of the Knight Street Bridge in Metro Vancouver,” in: GeoMontreal, Geoscience for Sustainability, 66th Canadian Geotechnical Conference and 11th Joint CGS/IAH-CNC Groundwater Conference, Montreal, Quebec, September 29-October 3, 2013. Montreal: Canadian Geotechnical Society.

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