Battery Street Tunnel Materials and Corrosion Testing

The Battery Street Tunnel (BST) is the northern extension of the Alaskan Way Viaduct (SR 99) in Seattle, Washington. BST is a cut–and-cover box tunnel with walls constructed of reinforced concrete cast around driven steel H-piles.  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. This paper provides the results and findings of this study.