The wave felt like an enormous ocean swell, except that I was nowhere near the water. It was January 17, 1994, hours after the 6.7 magnitude Northridge Earthquake struck, when a 5.0ish aftershock sent me and a dozen other onlookers scurrying for safety from our vantage point atop a concrete bridge from where we could see several derailed train cars below. On that day (the best of my 10-year career as an engineer), I observed houses, apartment complexes, parking garages, businesses and bridges that had failed in expected and unexpected ways. Later, from the safety of my home in San Diego, I spent hours over a period of months looking at photos of the damage, especially of structures made of wood–most relevant to my then job, and bridges–at a short-lived but much-loved stint at a bridge design firm, I had learned the basics seismic retrofit of bridges.
After the magnitude 6.9 Loma Prieta earthquake on October 17, 1989, WSDOT “asked engineers from the Washington State Transportation Center at the University of Washington to study the viaduct’s seismic vulnerability.” Catastrophic failure of the Cypress Street Viaduct’s columns, “a 1.6-mile-long (2.5 km), raised two-tier, multi-lane (four lanes per deck) freeway constructed of reinforced concrete” raised concerns about the potential collapse of the similar in several ways Alaskan Way Viaduct. “The Transportation Center report explained that the viaduct was built before the 1971 San Fernando Earthquake, also in California, that led to changes in construction practices. The viaduct is a strong structure, but it has too little transverse reinforcement, too little overlap in the splices at joints, and is at risk of excessive stress on the column foundations because of the high likelihood that the soil around the foundations and pilings, which had been brought in to fill behind the Alaskan Way seawall in the 1930s, would be subject to destabilizing liquefaction.” The Summary Report, published in July of 1995, confirmed what engineers had suspected: the Viaduct was structurally vulnerable to a significant seismic event.
“The viaduct was built in three phases from 1949 through 1959, with the first section opening on April 4, 1953.” “In the mid-1960s it carried 88,000 vehicles per day. When the Seattle Freeway opened, that number dropped to about 54,000, where it stayed for some time and then began to climb again as the region’s population grew.” “By the end of the 20th century, it was among the state’s busiest and most important sections of highway, carrying 110,000 cars each day.” “In February 2001, a 6.8 magnitude earthquake struck Seattle. When the shaking stopped, sections of the viaduct had sunk several inches. Crews stabilized the structure, but engineers agreed that had the quake lasted a few moments longer the viaduct would have collapsed…In January 2009, leaders from the state, county, city and port recommended a bored tunnel – along with a host of other improvements – to replace the waterfront section of the viaduct.” What they couldn’t know then was that this replacement wouldn’t be open for traffic for another ten years.
A July 2016 AP article summarizes the planned versus actual costs and construction schedule of the 99 Tunnel, “The troubled project to replace an aging double-decker highway bridge hugging Seattle’s waterfront with a tunnel faces $223 million in cost overruns…originally budgeted at $3.1 billion, because of repeated delays…the tunnel boring machine broke down in late 2013, leading to a more than two-year delay while it was fixed…The original completion date for the tunnel was the fall of 2015 but the opening of the double-decker highway project is now projected for early 2019.” In addition, Seattle Tunnel Partners, “is seeking $642 million for delays and repairs after Bertha [the boring tunnel] broke down.” If successful, this would put the actual project cost at 28% over budget.
It’s been 25 years since I ran for (what felt like) my life off of that bridge on the day of the Northridge Earthquake and my fascination with the performance of structures under seismic loads hasn’t diminished. When I pass a bridge, I look for the tell-tale signs of seismic retrofit, like cylindrical steel casings around columns and restraining devices designed to prevent bridge decks from falling from their supports. The Washington State Department of Transportation’s Bridge Seismic Retrofit Plan spells things out for our state (1) prevent deck collapse, (2) address lack of redundancy in single-column-pier bridges and (3) jacket multi-column pier bridges with steel casings. Victor Gray, engineer and leader of the Viaduct Preservation Group led an unsuccessful attempt for retrofit of the viaduct over replacement, citing cost savings and the retention of the original six lanes versus the bored tunnel’s reduction to four lanes.
On February 2, 2019, my sister and I and thousands of others participated in the Tunnel to Viaduct 8K. Race morning, we walked in darkness along Seattle streets towards the Space Needle, where we were to wait until our 8:00 am assigned start time. Corrals designated from 1 to 12 were supposedly (but not actually) based on pace, and supposedly (but not actually) set to start every six-minutes after the first wave–scheduled for 7:30 am. Runners and walkers of all ages, shapes, and sizes chatted with friends and snapped selfies while waiting for their corral to advance to the tunnel. Damp, cloudy skies promised rain.
Finally, at 8:45 am, organizers us in Corral 6 towards the tunnel entrance and sent us on our way. My sister and I reached the Mile 1 sign earlier than expected. Our GPS watches were useless so far underground, but we knew we’d be exiting the tunnel just after Mile 2. We ran along surface streets to the entrance to the Viaduct near Columbia Street and from the exit until we entered the one-third-mile-long, dark and damp Battery Street Tunnel. Upon exiting the BST, we returned once again to surface streets, made a couple of left turns, then a right, passed a long line of green and white porta-potties, ran up a barely noticeable hill and crossed the finish line. As we exited the finish area, the last wave prepared to start. Results indicate that there were 25,244 finishers (57% women). Dan Sloat came in first, completing the course at a 5:07 min/mi pace. Ruth Perkins was the first woman to finish, at a 5:57 min/mi pace. We finished at a respectable 9:00 min/mi pace.
After the all is said and done, my one and only feeling about the Alaskan Way Viaduct’s demise of total and complete annihilation at the hands of demolitionists is–relief. The structure was vulnerable to a significant seismic event for over 60 years, during the entirety of its existence. That it was taken out of service before The Really Big One hits Seattle should bring some level of comfort to all Seattleites.