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May 22, 2006
While I understand the spirit behind the suggestions by some structural engineers that retrofitting the viaduct is a viable alternative, there are some pretty big issues that they fail to address.
Steel sheet piling is a short term solution to replacing the aging seawall. It does not have a very long life cycle, and a rusting steel ribbon on the waterfront will neither present a good image of Seattle, nor will it provide a positive environmental image. More importantly, it doesn't address the rotting mass of wooden piers that currently struggle to hold up Alaska Way.
Reinforcing the columns of the viaduct doesn't address the real problem either. The viaduct isn't shifting 4 inches to one side because the columns don't meet earthquake standards, although by all accounts they don't come close. The problem stems from the tens of thousands of rotting piers beneath the viaduct and Alaska Way that were installed at the turn of the century when Alaskan Way was a long wharf supporting eight parallel rail lines. Which is the heart of this whole problem.
The rotting piers will have to be addressed at some point. With holes large enough to fit people in, any long term solution on the waterfront will require digging up the entire Alaskan Way and filling in with stable soil. If we fail to address it, we risk sinkholes along a heavily traveled commute and transportation corridor.
Those holes have also weakened the concrete seawall, providing no solid back to balance the battering pressure of waves and tides. Choosing an alternative that doesn't address these buried piers, such as a surface road or short term reinforcing, means that we will be facing a much more costly fix down the road.
The tunnel option is a nearly fully funded option that addresses the serious issue of a collapsing Alaskan Way, money that cannot be used on reinforcing the existing structure or an Aurora-style surface street. The tunnel option provides the construction efficiency of incorporating a seawall, elimination of the rotting piers, and a high capacity highway all in one structure.
We will have to dig out the waterfront eventually, so instead of filing it back in with dirt, building a viaduct in the ground at that time just makes sense. If it is built beneath Alaskan Way and adjacent to the viaduct, it can be built with little disruption to the existing commute, unlike a new viaduct structure.
As for cost, considering that all of the money proposed so far is tied to either a new viaduct or a tunnel, any discussion of cost should be on the basis of how much the local region will have to contribute to the final solution. With that in mind, all of the proposed options result in costs to the region of $500 million to $1 billion. Only one proposed solution addresses all of our problems along the waterfront — from the seawall, to the rotting piers and the need for transportation infrastructure that won't gridlock our fair city.
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