A simple and cheap viaduct fix

After the Nisqually earthquake, which occurred nearly five years ago, the state Department of Transportation retained T.Y. Lin International to review the Alaskan Way Viaduct. A report was issued that predicted that a 210-year-magnitude earthquake (twice the strength of the Nisqually tremor) has a 1-in-20 chance of occurring before 2011.

Now, five years later, we are offered viaduct solutions that would take up to 10 years to complete.

The DOT and the city of Seattle offer two choices: a tunnel, at a cost of $4.1 billion; or, a rebuild of an elevated structure at a cost of $3.1 billion. Both appear unacceptable because of the cost and the nearly 10 years to complete, not to mention the total disruption of traffic during that time. The traffic disruption is estimated at $140 million each year. This cost is not mentioned in the state's estimate.

We have offered a solution to brace the existing viaduct and add dampers to protect against future earthquakes. This solution has been ignored by the DOT for the last 18 months, on the grounds it was presented too late to be considered.

The existing viaduct, starting from the Battery Street Tunnel, consists of some 64 three-span units over 2.2 miles. Only two or three of the units were damaged and those have been repaired. The northern part of the viaduct was opened in 1952. The section south of King Street was opened in 1956. The life of a structure can be 80 years or more if it is maintained, as evidenced by many structures throughout the country.

The advantage of bracing and dampers is that they can be installed while the viaduct remains open to vehicles. This solution would eliminate traffic disruption, and maintain waterfront businesses and car-ferry traffic. At $600 million, the retrofitting would be a fraction of the cost of a new tunnel or rebuild.

The bracing can be designed to resist twice the forces of the Nisqually earthquake. We propose to stabilize the ground below the viaduct by jet grouting. Grouting consists of injecting a cement compound that mixes with the soils to form a solid soil mass.

The new bracing consists of structural steel diagonal tubes and plates connected to existing girders and columns. The columns and foundations would also be strengthened. The diagonals would transfer the earthquake lateral loads from the upper decks to the foundations, eliminating the need to rely upon any weakened girder-to-column connections.

The state and the city maintain that the seawall is vital to the safety of the viaduct. North of Pike Street, the viaduct is situated on glacial till, which is not vulnerable to liquefaction. Where the viaduct parallels the seawall, it is far enough away to be stabilized independently of the seawall.

The seawall is some 8,000 feet in length, with only 3,000 feet near the viaduct. We have no problem with the seawall restoration but believe that can be done separately and is a city responsibility. The bracing work can start almost immediately and can be completed well short of 10 years. By breaking the work into sections for design and construction, the work can be expedited. In addition to our estimate of $600 million for the viaduct bracing, the seawall work would cost about $200 million. We have asked the state to do an independent study, using outside engineering firms, to verify the costs, but to no avail.

Our concerns about the tunnel are many. Besides the cost and potential for serious overruns, our concern is for safety. The tunnel would be built across the Seattle Fault and would suffer damage during an earthquake and a likely tsunami in Elliott Bay that could flood the tunnel.

The tunnel eliminates access to downtown; the face of the tunnel wall moves into Elliott Bay beyond the existing seawall; construction disrupts all waterfront activity; a tunnel requires a new ferry pier and has no provision for future traffic growth.

A rebuild requires tearing down the existing structure at a cost of about $150 million and replaces it with a more-bulky structure. As with the tunnel, traffic capacity would be about the same as now.

The solution that we propose would provide for another 30 to 50 years of service or more if maintained. During that time, long-range transportation needs can be determined and agreed upon. And the billions of dollars saved could be used to address other critical regional transportation projects.