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New technology makes North American debut on a Ballard tunneling project

Summary

Two public meetings will provide status updates on a King County project to build green stormwater infrastructure to control combined sewer overflows (CSOs) from the Barton Pump Station in West Seattle.

Story

Sophisticated engineering will make construction a smoother, quieter experience for neighbors of King County’s Ballard Siphon Project to replace a 77-year-old wooden sewer line beneath the Lake Washington Ship Canal.

Using state-of-the-art excavation technology for the first time in North America, King County and its contractor, James W. Fowler Company, will build a 30-foot-diameter, 145-foot-deep launching portal for a tunnel boring machine, without requiring pile driving or ground freezing to stabilize the structure walls. The Vertical Shaft Machine, or VSM, was developed by the European company Herrenknecht.

In addition to being less disruptive than traditional shaft construction, VSM works well in tightly confined city spaces and in areas with difficult soils and high water tables. The machine is also powered by electricity and doesn’t require the continuous operation of noisy diesel generators.

To build the shaft with the VSM, an initial section is excavated and a concrete ring wall is built to support the machine, which is then lifted in with a crane and assembled in place. Winches enable an operator to remotely move the machine up and down, and precast concrete segments are then installed to structurally line the shaft as the VSM continues to excavate.

The shaft is kept full of water during excavation to help balance groundwater levels and to allow the excavated material to be pumped out and sent through separation equipment for disposal. The machine is capable of excavating and lining three to 15 feet each day. A demonstration video is available through the International Tunneling and Underground Space Association website (external link) at http://uww.ita-aites.org/index.php?id=782.

The shaft is scheduled to be completed this June. King County expects to launch a tunnel boring machine in September to build an 10-foot-diameter, 2,000-foot-long tunnel between Shilshole Avenue in Ballard and Commodore Way in Seattle’s Interbay neighborhood.

In service since 1935, King County’s Ballard Siphon carries up to 60 million gallons of wastewater each day underneath the Ship Canal from north Seattle to the West Point Treatment Plant in Magnolia.

King County has budgeted $38 million for the project. A low-interest loan by the Washington State Department of Ecology will provide more than half of the funding.

When complete in 2014, the project will increase system reliability while helping to control combined sewer overflows during heavy rain, helping to protect water quality in the Ship Canal and Salmon Bay.

To learn more about the Ballard Siphon replacement, visit the project website at http://www.kingcounty.gov/environment/wtd/Construction/Seattle/BallardSiphon/Library.aspx.


People enjoy clean water and a healthy environment because of King County's wastewater treatment program. The county’s Wastewater Treatment Division protects public health and water quality by serving 17 cities, 17 local sewer districts and more than 1.5 million residents in King, Snohomish and Pierce counties. Formerly called Metro, the regional clean-water agency now operated by King County has been preventing water pollution for nearly 50 years.

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Note to editors and reporters: Visit the WTD Newsroom, a portal to information for the news media about the Wastewater Treatment Division, King County Department of Natural Resources and Parks: http://www.kingcounty.gov/environment/wtd/Newsroom.aspx

Related information

Ballard Siphon replacement project

King County Wastewater Treatment