Thursday, July 14, 2011

I-405 Countdown to the Closure - Demolition Information

Dear Partner,

Some of you have asked how the Mulholland Bridge will be demolished. Well, now you have it! Read on…

No explosions or columns collapsing in a cloud of dust this weekend as workers demolish the southern half of Mulholland Bridge. Instead, humans and machinery will perform a carefully orchestrated ballet, resulting in the 51-year-old bridge being pecked apart by the equivalent of multi-ton woodpeckers.

Consequently, the south half of the iconic three-span box girder bridge will be steadily chipped away over 53 hours July 16-17, not 3 seconds.

For over a year, Kiewit Infrastructure West, the project's contractor, has developed a 154-page demolition plan—approved by Caltrans and Metro—that breaks the work into precise, 15-minute increments, giving the contractor schedule milestones as it manages its progress toward reopening the freeway for early morning rush hour traffic on Monday, July 18.

The demolition process will begin Friday evening, July 15 when work crews begin closing freeway on- and off-ramps between the I-10 and U.S. 101. This may happen as early as 7pm. Crews will then begin closing freeway lanes one by one on both sides at 10pm to close the freeway completely by midnight. The Mulholland Bridge will be closed as well.

Fifteen pieces of heavy construction equipment (with another five on standby) and an army of 100 demolition workers and support staff will begin deconstruction.

Starting at midnight, dirt will be hauled onto the 405 freeway underneath the Mulholland Bridge to form a cushion four feet high onto the freeway roadbed. The dirt will catch falling debris and prevent them damaging the freeway surface.

At approximately 2am on Saturday morning, workers will use a large diamond-bladed saw to cut the bridge top deck. Other workers will cut slots in the southern side of the bridge. During demolition, workers will perform vibration monitoring and other tests to ensure the structural integrity of the northern side of the bridge.

At approximately 5am, as many as four "hoe rams" will begin to chip away at the south side of the bridge, creating approximately 2,200 cubic yards of concrete. Two hoe rams will be stationed on the bridge deck starting in the center working toward each end. Two hoe rams will work on the ground, also starting in the center and working toward both ends. The hoe rams will deliver between 1,200 and 7,500 foot pounds of power to break concrete from the bridge. Operators in these machines will be able to deliver between 300 and 600 blows per minute to create pieces no bigger than a basketball or microwave oven.

Later, the concrete will be pulverized and recycled as "aggregate base" which forms the foundation for the new lane of traffic created by the project.

While the hoe rams steadily chip away at the concrete, other workers using long-handled oxygen/acetylene torches will cut the steel rebar from the bridge deck amid a crackle of sparks. The rebar will also be recycled.

Once the demolition is complete, an army of laborers will clean the edge of the bridge to ensure that no particles fall on the traffic below.

This demo work will last until 2am Monday morning when crews begin their final cleanup to ready the freeway for reopening by 5am. Between 10 and 20 large trucks and several front end loaders will be used for the cleanup. The freeway surface under the bridge will be cleaned by a parade of street sweepers, inspected, and finally restriped with fresh paint. Ramps and freeway connectors will reopen by 6am.

A full description of the demolition process is available here.

Still photos of the demolition will be available throughout the weekend at www.metro.net/405.

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