Abstract
Abstract Since 1993, construction has been underway on the Westside Light Rail Project, a 29-km extension of Portland, Oregon's existing light rail transit system. The extension includes a 4.6-km long, twin tunnel section through Portland's West Hills, and an underground station servicing the City's Washington Park. Washington Park Station, constructed in Columbia River Basalt at a depth of 79 m, will be the deepest transit station in North America. The station is laid out in a double platform binocular configuration. The platforms are 62 m long, and the lobby, passageway and platform caverns range in height from 6.4 to 8.8 m. The station caverns were excavated by drilling and blasting in multiple headings. Initial ground support for the station caverns was provided by rock dowels and shotcrete, with spiling used extensively for pre-reinforcement. The final liming consists of reinforced, cast-in-place concrete. Access to and from the surface is provided by two shafts, which will each contain high speed elevators, emergency egress stairways, ventilation ducts and utilities. This paper discusses the geologic conditions, underground opening design, excavation methods, and initial ground support installation for Washington Park station.
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