GEOTECHNICAL BASELINE FOR THE SR 99 BORED DESIGN-BUILD ALASKAN WAY TUNNEL, SEATTLE, WASHINGTON

摘要

Washington State Department of Transportation has awarded a contract to designrnand construct a 17.5 m (57.5 foot) diameter bored tunnel at depths up to 60 m (200 feet)rnin the glacial soil under downtown Seattle, Washington. Geotechnical investigationsrnresulted in a baseline report, data report and characterization report. The GeotechnicalrnBaseline Report (GBR) and Geotechnical Data Report(GDR) were provided as part ofrnthe contract documents and were an integral component of the risk sharing aspects ofrnthe design-build contract. An initial assessment of over 300 buildings was conductedrnto identify those most sensitive to settlement. Mitigation measures include compensationrngrouting for specific buildings. Extensive construction monitoring is planned. Thernproject also includes cut-and-cover construction at south and north portals for transitionrnbetween side-by-side roadways and stacked configuration roadway in the boredrntunnel. An initial assessment of more than 300 buildings along potential tunnel routesrnwas conducted to identify those most sensitive to settlement. Prequalification of tunnelrncontractor teams started in late 2009 and resulted in two proposals. The Seattle TunnelrnPartners (Dragados and HNTB) were awarded the project for $1,089,700,002 million.rnThis paper will discuss the considerations that went into development of the GBR, constructionrnmonitoring and technical requirements for the bored tunnel.