大林組
Sound Transit awarded the tunnel-boring contract to the Obayashi Corporation, one of the largest Japanese general contractors, for $280 million with a $20 million contingency, an estimated $42 million more than expected by the agency. Obayashi and the Beacon Hill Constructors were the only firms to compete for the Beacon Hill Tunnel and Station contract, the latter bidding $305 million. Beginning in March 2005, workers excavated of two , vertical shafts using a technique utilizing a concrete "slurry wall" cylinder and pumping in cement grout to stabilize soils. The tunnel itself was mined using a tunnel boring machine sporting a diameter drill, with 150 blades rotating at 1.5 rpm whilst moving at a maximum of per day, custom-built for the project by Mitsubishi Heavy Industries in Kobe, Japan. Nicknamed the "Emerald Mole" during a contest for children in late 2005, the drill was launched during a public ceremony on January 18, 2006 held at the west portal of the tunnel on the west side of Beacon Hill, below Interstate 5, where the TBM started excavating. Construction at the station site was briefly interrupted for an hour in May by 17 protesters demanding contracts for businesses owned by African Americans, the only such incident at the construction area.