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Geotechnical Work to Begin on Knik Arm Crossing’s Government Hill Tunnel

Subsurface work needed to construct cut and cover tunnel under Erickson Street

(Anchorage) – The Knik Arm Crossing took another step toward construction today when the Knik Arm Bridge and Toll Authority authorized geotechnical work to begin on Government Hill for a future “cut and cover” tunnel.  Work will include exploring the subsurface conditions to 50 feet below the ground surface, and identifying the soil and groundwater conditions.  The subsurface exploration will also include identification of any contaminated soils and the evaluation of seismic conditions.

The 800 foot long “cut and cover” tunnel is part of the selected Erickson Street Route for the Anchorage side of the Crossing.  The 6-lane tunnel places all through traffic below the neighborhood in order to mitigate for the visual, noise, and air quality impacts to the surrounding area.  The tunnel is being constructed with six lanes to minimize the disturbance to the neighborhood when expansion of the roadway is needed in the future. 

Because the tunnel has a cover, or lid, it allows the neighborhood to remain cohesive.  Additionally, the Federal Highway Administration’s Record of Decision identifies that additional park amenities can be included on the tunnel lid, including green space, trails, parking, playgrounds, and general interpretive signs of the neighborhood.  These amenities will be developed by the contractor and community representatives through a collaborative process designed to identify improvements which fit the unique local setting, also known as a Context Sensitive Solutions process.

“The geotechnical information will allow the successful proposer to design and build the tunnel to specific site conditions.” Said Judy Dougherty, deputy executive director for the Knik Arm Bridge and Toll Authority.  She added “the information will allow the three teams vying for the project to factor this information into their proposals.”

Three consortiums have been short listed to partner with the state on the bridge project after a “Statement of Qualifications” phase in 2011.  These teams are now allowed to compete for the contract through a competitive proposal process, which is expected to begin next spring after passage of legislation establishing a project reserve. 

Geotechnical work is possible in the Erickson Street area because the Authority owns the land over the future tunnel.  Shannon and Wilson Inc., a national geotechnical and environmental firm with offices in Anchorage, will conduct the field studies and subsequent reporting.  The work will take several months to complete and will cost approximately $50,000. 

 

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