The Fraser River Delta in Metro Vancouver is one of the most populated areas of significant seismic hazard in Canada. The low-lying delta is underlain by deep unconsolidated Holocene deposits of fluvial sands, deltaic silty sand, and marine silts and clays. Seismic ground motion amplification and liquefaction are well-recognized hazards that present significant challenges for infrastructures. Spurred by the 1989 Loma Prieta earthquake, British Columbia embarked on an ambitious seismic retrofit program of older bridges in the region, including many highway bridges in the Fraser Delta underlain by liquefiable soils. Seismic upgrade of existing bridges presents special risks and challenges, particularly related to site constraints and the need to maintain the bridge in service during remedial works. This paper summarizes the key issues and challenges faced in geotechnical seismic upgrades of bridges in the Fraser Delta in the last two decades. Examples of various ground improvement methods used in several seismic retrofit case histories are described and lessons learned outlined.
Sy, A. 2018. “Challenges in Geoseismic Upgrade of Bridges in the Fraser Delta, BC, Canada,” in Geotechnical Earthquake Engineering and Soil Dynamics V, June 10-13, 2018, Austin, TX. American Society of Civil Engineers (ASCE)