Tuesday, July 21, 2015

SR 18 in Auburn: What lies beneath?

A large rebar cage serves as the future
bridge pier’s structure.
By Caitlin Morris

During the weekend of July 25-26, on State Route 18 we will perform a complex and well-choreographed dance of machinery, dirt and water to install a 120-foot-long bridge pier for the future SR 167 southbound HOT Lane.

Passersby will notice cranes, drills, and 20,000-gallon tanks full of water and mud. While the scene may look very chaotic, all the action is really happening underground.

And the work will occur in an area about the size of a baseball diamond.

The bridge will eventually connect the north and south ends of the 8-mile-long SR 167 southbound HOT lane extension project, and will be 24 feet wide with retrofitting for future lane additions on either side.

In any kind of construction work, you start at the bottom and work your way up. Over the weekend, we will lay the foundation for the rest of the bridge. It’s the most critical step, and we’re trying to get it done in a very short amount of time.

Crews will work within a small construction zone.
Big Weekend Closure Ahead
To do all of the work, crews will shut down westbound SR 18 completely and funnel eastbound traffic to one lane at SR 167. Even if most drivers avoid the area over the weekend, we’re expecting increased travel time on and around SR 18 in Auburn.

Plan ahead, folks.

The weekend’s construction will take place in the 50-foot-wide space between the two existing SR 167 bridges over SR 18. A drill held by a large crane will bore a hole deep and wide enough to hold the 120-foot-long concrete cylinder’s 8-foot-wide diameter. In order to do that, we will need several 20,000-gallon tanks of water to maintain the hole’s stability as the drill works.

As the drill progresses, crews will haul off residual dirt, resulting in nearly 30 truckloads of materials that must make their way in and out of the small construction zone, while also avoiding detoured traffic. It’s all about taking the space we have and making it work.

Design eliminates several weekend closures 
The project requires rigid time and space constraints to spare commuters additional closures of the popular SR 18/SR 167 interchange. In the project’s preliminary design stages, engineers had the option of adding three shallower bridge piers, but opted for a larger, deeper pier that bears more weight. Reducing the number of piers allows crews to reduce three separate closures to one. Over a typical summer weekend more than 170,000 drivers pass through the SR 18/SR 167 interchange, making one closure the ideal option. A lot of engineering and coordination went into minimizing traffic impact.
The bridge pier will be 120 feet long with and 8 feet wide.

To complete the installation in one weekend, crews will rotate around the clock in a relay race of operations. On Friday night, crews will deliver 3-5 truckloads of materials that within hours will become the crane supporting the oscillating drill. At the same time, crews will begin excavation. As the oscillating drill moves deeper into the ground, crews will remove the residual dirt, simultaneously filling the hole with a water and clay mixture to maintain the hole’s structure. After crews excavate, they will place a large rebar cage in the middle of the shaft and begin pouring concrete to create the bridge pier’s cement cylinder. As the concrete fills to the surface, large pumps will catch the residual water and clay mixture refilling the 20,000-gallon tanks.

While traffic congestion may rise in the SR 18/SR 167 area over the weekend of July 25 and 26, drivers on eastbound SR 18 will get to catch a glance of this carefully coordinated operation. We will post photos of this engineering feat to the project’s Flickr site.

1 comment:

Priyesh said...

Thanks for the heads up!

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