Replacement tunnel

Started: 2019-02-17 11:55:22

Submitted: 2019-02-17 19:05:56

Visibility: World-readable

2 February 2019: In which the intrepid narrator walks (again) through the SR-99 tunnel under Seattle

After running through the SR-99 tunnel under downtown Seattle, I returned to Seattle Center in the afternoon, with my family, to take a second look at the party celebrating the opening of the new tunnel and the closure of the Alaskan Way Viaduct.

We ate lunch in the food court inside the armory, then walked past the Space Needle and the Museum of Pop Culture to the new tunnel's north portal, where the surrounding blocks had been blocked off for the festival celebrating the tunnel. We ended up in a long line of people snaking towards the tunnel portal. Most of the people in line had timed tickets allowing tunnel admission, but it appeared likely that there was some provision for those who showed up without timed tickets. (By the time I decided we wanted to visit the tunnel party, the only remaining timed tickets available were late in the afternoon and we thought that was too late to get back in time to get Julian to bed at a reasonable hour.) When we turned onto the tunnel on-ramp we found the line for people without tickets -- which turned out to be much shorter than the line for people with tickets. There was one person enforcing flow control at the bottom of the on-ramp, within view of the tunnel portal, who conceded that the system of offering immediate admission to queue-jumpers without tickets was weird but that's what it was so we were free to join the crowd and enter the tunnel.

Since my first visit to the tunnel earlier that morning, the tunnel had been outfitted with barriers enforcing pedestrian lanes: one lane on the right for return walkers, one lane at the left for police on bicycles, and a main lane in the middle for pedestrians walking into the tunnel.

Shortly after we set foot in the tunnel I saw the police in action, breaking up what seemed to be a fist-fight triggered by two dogs fighting each other.

After that brief excitement, the rest of the tunnel was comparatively uneventful. We decided to keep walking the two miles through the tunnel, rather than taking the u-turn exit provided. (After the turn-around point, the only way out was through.)

Throughout the tunnel, interpretive signs pointed out various interesting features of the tunnel, identifying the geography at street level. One sign pointed out where the tunnel was the lowest below ground level, but at that point the tunnel was still descending to its own lowest point; this apparent dissonance caused by the hilly Seattle downtown. (I did note that the interpretive signs did not identify the point where tunneling was stopped for two years to excavate, repair, and replace Big Bertha's tunneling head, a few thousand feet from its starting point in SoDo.)

Walking through the tunnel, snaking gently under the streets and buildings below downtown Seattle, gave me the opportunity to study the tunnel's safety features in greater detail. All of the emergency exits were closed, but one of the small louvers covering the window from the area of refuge into the main tunnel was open, giving a chance to look into the room behind -- and study the precast concrete segments making up the tunnel wall, including the bolts where the segments were attached to each other.

On the other side of the tunnel, near the lowest point of the tunnel, where the crown of the tunnel was 95 feet below sea level, the negative-pressure vents designed to evacuate smoke or other hazardous fumes from the tunnel were open, giving a similar view of the tunnel lining without the fireproofing covering the main ceiling of the tunnel.

Past the low-point of the tunnel, the roadbed gently ascended towards the south portal.

We kept walking, keeping pace with the crowd, and soon we emerged into the open air at the south portal in SoDo. The high-rise buildings of downtown Seattle were visible behind us, framed by the on-ramps forming the approaches to the tunnel portal.

Across the street from the off-ramp leading from tunnel's south portal we found another, smaller, festival with various booths from various organizations. One of the exhibits, from one of the civil engineering firms engaged in the tunnel's construction, showed a large cross-section of the tunnel, identifying the different soils the tunnel dug through in different colors, and included dirt and mud and clay from the tunnel excavation as a hands-on exhibit. The exhibit included test tubes and brightly-colored sand to make your own core sample. Calvin was not interested in making his own core sample, so I took the test tube and built one for myself. Julian, at least, was amused by the hands-on part of the exhibit and made his own core sample.

We caught a shuttle bus back to the north portal of the tunnel, running conveniently through the lower deck of the tunnel, which would handle north-bound traffic when the tunnel opened two days later. The lower deck of the tunnel had the same safety features as the upper deck, but the the features reversed sides: the hard shoulder and emergency exits were on the left side of the road, and the negative-pressure vents were on the right side of the road. The ceiling was flat, supporting the road surface of the upper deck.

Back at the north portal, we stopped by the exhibits and found one, also set up by the main civil engineering contractor, with a soapbox car built in honor of Big Bertha, and a couple of child-sized interactive exhibits demonstrating how the precast concrete sections of the tunnel were installed, and how the tunnel turned under the ground by using the design of the precast concrete sections to point the tunnel in different directions.

Our last stop was the Lego tent, which showed a Lego model of the cross-section of the tunnel (finally answering my lingering questions about the arrangement of the road and escape spaces inside the tunnel) and a large diorama of the future Alaskan Way boulevard with the tunnel conveniently located immediately under the road.

Part of the Lego exhibit was interactive: guests were invited to build their own vehicles at side tables and put them on the roads. Calvin built a vehicle while Julian played with the Duplos on the side of the tent (because apparently someone else's Duplos are always more interesting that one's own).

We stopped by a French bakery in Belltown for a snack before heading back to our house in Wallingford.

I've read about infrastructure openings where new roads (or bridges, or tunnels) are opened to pedestrians before opening to traffic, but I'd never had the opportunity to participate -- until now.

For more pictures of the unnamed SR-99 tunnel, see Photos on 2019-02-02.