Thursday, April 27, 2017

How do you rehabilitate nearly 22 miles of I-5?

By Tom Pearce

A few years ago my family and I were traveling through rural western Illinois on Interstate 88 when we came across a construction zone. The highway was reduced to one lane; the other lane and shoulder were torn up all the way down to dirt to rebuild it. This went on for 20 miles!

That is one long, continuous stretch of roadwork to drive through, believe me.

Well, we just started the first of two projects that will rehabilitate nearly 22 miles of northbound I-5 from Kent to the Ravenna neighborhood in Seattle and while it’ll take three years, don’t worry, we’re not going to reduce I-5 to one lane for months on end.

Instead, by working at night and on weekends, we’ll use different methods to #ReviveI5:

Panel replacement: After the concrete panel is removed, the ground is compacted to provide a stable base for the new panel.

Replace broken concrete panels
Concrete panels will eventually break – hundreds have between Kent and the Duwamish River. To replace these, one night we use a big circular saw to cut the concrete. The next night we dig out the panels and pour new ones. In the past we’ve found we can typically do about three to six panels a night.

It’s the same with the section between Martin Luther King Jr. Way and Northeast Ravenna Boulevard in Seattle. Along one three-mile stretch between the West Seattle Freeway and Seneca Street, all of the panels that aren’t part of bridges will be replaced.

SB paving: After the concrete is cracked and seated (compressed), 8 inches of asphalt will be paved on top of it.

 Asphalt repaving
In SeaTac and Tukwila, we have too many broken concrete panels to replace them individually – it would take years. Instead we’re going to repave with asphalt using a process called crack, seat and overlay, just like we did last year on southbound I-5 in the same area. This allows us to repave a large section much more quickly.

Eliminating ruts
If you put pressure on something for long enough, it’s going to wear away. That’s what car and truck tires have been doing to I-5 for more than 50 years. Now we have ruts in the concrete lanes, which can collect water and reduce traction. To get rid of the ruts, we grind off a thin layer of the higher, unworn part of the concrete, leveling the roadway.

Expansion joints
These metal connectors on bridge and elevated sections of the interstate allow the roadway to expand and contract as the weather changes. They wear out after a couple of decades. It’s better to schedule replacement during off-peak hours than have them break, say, in the middle of a peak commute, which requires emergency repairs. We’ll replace 37 expansion joints in Seattle, mostly between the West Seattle Freeway and Seneca Street, and eight at Interurban Avenue and the Duwamish River Bridge in Tukwila.

The next several years will be a challenge as we #ReviveI5. In the end, we’ll have a lot of renewed interstate to see us through the next several decades. And unlike what I saw in Illinois, we won’t reduce I-5 to one lane for several months to do it.

This is the second in a four-part series on highway preservation work starting this month on northbound I-5 from Kent to Seattle. Part one covers the history and development of these projects.