SR-99 Alaskan Way replacement
Seattle, USA
TBM EPB
Construction method
2.688 m
Excavated length
15.85 / 17.48
Internal diameter / excavation
1 TBM world record
TBM number
50 m below sea level
Depth
The SR 99 Alaskan Way Replacement project involved the construction of a 2,688 m urban road tunnel beneath downtown Seattle using the world’s largest EPB tunnel boring machine at the time of construction.
The scheme replaced a major urban transport corridor through a double-deck tunnel with two lanes in each direction arranged on two levels. The alignment runs beneath the city centre and passes below landmark buildings, reaching a maximum depth of 50 metres below sea level.
The tunnel boring machine, of innovative design and Japanese manufacture, incorporated state-of-the-art technologies for cutter replacement and robotic systems, enabling successful excavation under highly demanding geotechnical conditions.
The tunnel lining consists of universal precast concrete segment rings, 60 cm thick and 2 metres long, achieving a final internal diameter of 15.85 metres.
The project reinforces Dragados’ expertise in large-diameter tunnelling and underground infrastructure delivered beneath highly complex urban environments
Project data
Project data
·
2,688 m urban tunnel
·
World's largest EPB TBM at the time
·
17.48 m excavation diameter
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15.85 m internal diameter
·
646,000 m³ excavated
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Double-deck road tunnel
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Up to 50 m below sea level
·
60 cm thick precast concrete lining
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World-record EPB excavation diameter
·
Completed in 2019
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