SAR, the design-build contractor for the SkyTrain Millennium Line, hired Ausenco Sandwell to conduct a value engineering review of the Millennium Line substructures comprising columns and caisson foundations with the objective of reducing construction costs. SAR reviewed the costs of alternative foundations and determined that caissons would be the most cost competitive. However, they decided to investigate potential savings on the construction costs of the columns and caissons. Ausenco Sandwell reviewed the design criteria and performance of the structures and in particular displacements under gravity, operating and seismic loading. SAR agreed to Ausenco Sandwell’s recommendations for a new design criteria and finite element computer modelling to investigate the damping effects of the soil during the seismic design event. The model’s results suggested that the soil damping effects had been underestimated in the original design. Ausenco Sandwell’s investigation and recommendations resulted in significant reductions in the reinforcement in the columns and caissons, and in some cases, a reduction in the caisson diameter, all of which reduced SAR’s construction costs.

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