09227 Battery Street Tunnel Materials and Corrosion Testing

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Product Number: 51300-09227-SG

ISBN: 09227 2009 CP

Author: Phil Simon, Steven Daily and George Inverso

Publication Date: 2009

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The Battery Street Tunnel (BST) is the northern extension of the Alaskan Way Viaduct (SR 99) in Seattle, Wash. BST is a cut and-cover box tunnel that is 2,100 ft. (640 m) in length, with walls constructed of lightly reinforced concrete cast around driven steel H-piles. Plans and documents for construction of the tunnel were approved in May 1952, and construction proceeded shortly thereafter. BST is now considered to be at its structural design life, which is assumed to be 50 years. The tunnel currently has no significant signs of structural distress; however, theoretical calculations based on limited field-derived corrosion rates predict loads may substantially exceed the design capacity in some locations as the tunnel approaches 65 years of use. Corrosion rate measurements of the steel H-piles were an integral part of a recent materials and corrosion testing program. The study involved assessing the current corrosion condition of the piles and the surrounding reinforced concrete, estimating the corrosion rate and remaining service life of the piles, and determining maintenance and repair options during the desired service life of the tunnel. To assess corrosion rates and estimate service life, linear polarization resistance (LPR) measurements were taken of the steel piles embedded in concrete, atmospherically exposed surfaces in areas of spalled concrete, and piles exposed directly to the soil environment. The latter was accomplished by inserting LPR probes through core holes in the tunnel wall. This paper provides the results and findings of the study, with special emphasis on the half cell potential measurements, LPR corrosion rate testing and the chemical and physical properties of the soil and concrete.

Keywords: corrosion rate, design capacity, service life, linear polarization resistance (LPR)