ABSTRACT
The Lions Gate Bridge is a 1.5km long, three-lane suspension bridge connecting North and West Vancouver with the City of Vancouver. The bridge is currently being considered for renovation and seismic upgrading. The southern foundations, on the Vancouver side of the bridge, are founded on very dense glacial till and sandstone bedrock, while the north shore piers and approach viaduct footings are founded on fluvial deposits of sand, gravel, cobbles and boulders of approximately 50 meter depth. The southern very dense soils are expected to move with the design earthquake motions, while the looser fluvial soils will amplify the earthquake ground motions and some local zones may liquefy. Numerical analyses, mainly using the program FLAC, were key parts of the seismic upgrade design. Analyses conducted using FLAC included a dynamic response analysis of the massive north anchorage, assessment of the consequences of localized soil liquefaction, and assessment of foundation stiffness and bearing capacity. The results of the numerical analyses indicated that differential displacements between the north anchorage and free-field ground motion were nominal (less than 16 mm), and that the sporadic liquefaction under the north anchorage and around the north main pier would not cause excessive deformation of the foundations. The analyses did show that pockets of liquefaction below the viaduct footings may result in excessive footing settlement.
