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FRASER HEIGHTS BRIDGE – GEOTECHNICAL CONSIDERATIONS FOR TOP-DOWN CONSTRUCTION ON DIFFICULT SOILS
Session: Foundations I / Fondations I
Brian Hall, Tetra Tech EBA (Canada)
Ali Azizian, Tetra Tech EBA (Canada)
David Harvey, Associated Engineering (Canada)
The Fraser Heights Bridge was constructed span-by-span, using a top-down approach, to satisfy the environmental obligations to minimize the impact on an environmentally sensitive wetland. Because of highly variable subsurface conditions, driven pipe piles supporting the bridge extended to almost 45 m depth on the east, but on the west where glacial till-like material was shallow, it was difficult to drive the piles sufficiently deep to obtain the necessary lateral support. Other geotechnical considerations included obstructions (tree trunks, boulders or glacial erratics); artesian pressure; high compressibility and seismic softening of silts, sensitive clays and peat; and, liquefaction and lateral spreading of hydraulically placed sand fills. Another factor related to top-down construction was the minimal time available to address unexpected geotechnical issues such as damaged or obstructed piles.
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