Needles Bridge Crossing: Managing Design Risk of a Long TermInfrastructure Investment

摘要

In 2003, the British Columbia Ministry of Transportation initiated a designrncompetition for the detailed design of the Needles Bridge crossing over Arrow Lake. Whenrnconstructed, this bridge will be the longest fixed link lake crossing in the province at arnlength of 1087 m. Arrow Lake was created in 1969 by the construction of the HughrnKennleyside Dam; and in 1967 a previous crossing design project was initiated butrnultimately was never advanced.rnThis paper describes the unique design methodology and risk management approachrnemployed during the recent design competition project, and presents some of thernsignificant challenges and constraints faced during alignment optimization. Geometricrndesign played a key role in the overall design economy of this large structure. Arnbathymetric survey was combined with conventional survey data and used to optimize thernsubsurface and shoreline horizontal geometry. The survey amalgamation improved thernoverall economy through minimized pier heights and optimal positioning of the navigationrnspan.rnGeotechnical and structural requirements were integrated early into the design process inrna true multi-disciplinary approach to design. Moreover, because the lake level is a functionrnof the downstream dam, the reality of significant water level fluctuations introducedrnadditional constructability constraints that required careful consideration by the designrnteam.rnThe resulting final design of the structure contains one horizontal curve and three verticalrncurves and is a successful blend of geometric, geotechnical and structural expertise. Thernrisk management strategies used throughout the course of the project significantlyrncontributed to keeping the design project on schedule and on budget. As a result, anrneconomical combination of superstructure, substructure, foundations and approaches wasrnintegrated together to provide a low life cycle cost alternative to the existing inland ferryrnservice on Highway 6 at Arrow Lake.