LINER SEGMENT DESIGN OF THE LARGEST TBM TUNNEL IN THE WORLD-ALASKAN WAY TUNNEL IN SEATTLE

摘要

Alaskan Way (SR 99) Tunnel in Seattle will be the world's largest TBM bored tunnel. The 17.1-m-diameter (56 ft), 2,835-m-long (9,300 ft), bored tunnel under downtown Seattle will reach depths of up to 66 m (215 ft). Along its alignment, the tunnel traverses through variable glacially overconsolidated soil deposits with high groundwater pressures of up to 5.2 bars. The tunnel will convey traffic underneath downtown Seattle and replace the 1950s SR 99 Alaskan Way Viaduct that runs along Seattle's waterfront. The double-deck structure had been deteriorating and was further damaged in the 2001 Nisqually earthquake. This paper discusses the geo-structural analytical approach and parametric evaluations conducted for the precast concrete segmental liner design. Geotechnical evaluations included numerical modeling of ground relaxation, existing and potential future building loads, and varying geologic conditions. Also discussed will be the implementation of the results of the geotechnical continuum analyses, performed for the varying soil conditions, on the structural design of the liner segments to meet strict service and strength requirements. The paper also describes the analytical procedure and design approach implemented for the seismic design of the tunnel.