The wood-stave wastewater siphons built in the 1930s beneath the bed of Salmon Bay between the Seattle suburbs of Ballard and Interbay urgently needed replacing. The capacity of the old lines had long been overtaken by population growth. The "Ballard Siphon Replacement Project" was established to this end.
The construction of the launch shaft for tunnelling under Salmon Bay marked the debut of Herrenknecht’s mechanized shaft sinking technology in the U.S.A. The VSM10000 vertical shaft sinking machine is superior to conventional shaft sinking in all material respects: greater performance and precision, less noise and improved work safety for the personnel. Within just 4 weeks from April 12 to May 16, 2012, the job was done. With a boring diameter of 9.8 meters, a 45 meter deep shaft was sunk at a rate of up to 2.6 meters per day. The Herrenknecht VSM easily handled its job below the groundwater table, which was especially high here in the direct vicinity of Salmon Bay. After the faultless premiere the VSM10000 traveled to Hawaii for the next project.
Another premiere took place during construction of the new sewage tunnel: for the first time in the U.S.A. a Herrenknecht machine in the small diameter range drove a tunnel with segmental lining. For the crossing under Salmon Bay the EPB2850 launched northwards from the VSM shaft. After 666 meters of tunnelling the machine reached the target shaft on August 19, 2013.
