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Project Date: 2011 - Active Project
BDHs PROJECT SOLUTIONS:
BDHs provided the prime contractor with solutions to a difficult situation. Our team was brought in during the tunneling operation to upgrade the manlocks that were found to be non-compliant with the applicable ASME/PVHO regulations. Ordering new manlocks in the middle of the operation would have caused substantial downtime on the high visibility project. BDHs completed an inspection of the system and were able to offer engineering solutions. The manlocks were refitted with new video systems, fire suppression systems, oxygen service, viewports, lighting, gauges and gas analysis was added. These upgrades allowed the contractor to gain a provisional PVHO certification on the manlocks, allowing their use on the project.
PROJECT BACKGROUND:
This project is part of Sound Transit’s University Link Light Rail extension and includes the Capitol Hill Station excavation and construction of twin 3,800 LF precast concrete segmental subway tunnels. The tunnels are being excavated utilizing a 21’-1” diameter Hitachi EPB TBM (Earth Pressure Balance Tunnel Boring Machine).
The Capitol Hill Station (CHS) shaft excavation is 540 FT long x 60 to 80 FT wide x 80 FT deep. The long walls of the shaft excavation are shored with soldier piles and wood lagging supported with tie-backs at multiple levels. The end walls of the shaft excavation are supported with shotcrete and soil nails at multiple levels. The CHS shaft excavation also includes the construction of a concrete base slab for the future subway station. This base slab is 8 FT thick and involves placing approximately 12,000 CYD of concrete.
The twin precast concrete segmental subway tunnels are approximately 3,800 LF each. The tunnel depths range from more than 130 FT to less than 18 FT where it crosses Interstate I-5, the major north-south artery in Seattle. The tunnels are being constructed at a down-hill grade of 5%. Nearly the entire tunnel alignment consists of horizontal & vertical curves with the tightest curve radius being only 550 FT.
Five cross passages are being constructed utilizing Sequential Excavation Methods (SEM) after the second tunnel is complete. A pump station will be constructed at the low point for each tunnel. The final phase of the project will include placing a concrete invert in the tunnels for the subway rail construction including permanent drainage piping and electrical lighting.
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