Demolition on the 405

Construction on Interstate 405 in the Los Angeles area was supposed to cause traffic to be snarled for hours on one of the world’s busiest freeways. It was supposed to be “Carmageddon.” Instead, the project ran around the clock and was completed well ahead of schedule.

Construction included widening I-405 by one lane in each direction. In the Sepulveda Pass, a 578-ft.-long bridge carried Mulholland Drive across the interstate. Since the I-405 was being widened, the bridge needed to be demolished and a new, longer bridge will take its place.

The Mulholland Bridge is four lanes wide, two in each direction. Two lanes in one direction needed to be demolished, leaving two lanes to carry traffic while construction proceeded to replace the demolished half. But the demolition was the tricky part. The deck couldn’t be torn down with conventional hydraulic breakers working on top, and dynamite was ruled out for the girders and two columns because a gas main crosses the bridge.

So to demolish the girders and columns, the main demolition contractor turned to Miller Environmental Inc., Anaheim, CA. Miller owns two Volvo EC460CHR high-reach demolition machines, which are 90-ft.-class units that could demolish the Mulholland Bridge by working from the 405 below.

“The high-reach concept is very European,” says Walt Reeves, segment manager, demolition, Volvo Construction Equipment. “In Europe, when they take down a structure, they process it as it goes down. That way you have less work at the ground level; you’ve pulverized the structure in place.”

Attacking From the Ground Up

A layer of dirt 4 ft. thick was placed on the 405 to protect the freeway from damage caused by falling concrete.

“By the time we were called in to work, it was about 4:00 a.m. on a Saturday,” says Gregg Miller, president and owner of Miller Environmental. “Our scope was to attack everything from the ground working at the high elevations. We had the two high-reach machines there, and there were some other activities on top of the bridge, breaking the deck. We broke the horizontal sides of the bridge and another machine would snip the rebar.

“We started in the middle, working about 85 ft. high,” Miller notes. “We worked our way toward each side of the bridge, using 6,000-lb. attachments off the ends of the high-reach machines. We ran continuous 12-hour shifts throughout the operation. Approximately 4,000 tons of concrete were removed from those two lanes. And we removed two columns, one on each side of the bridge. In the next phase, when we demolish the other half, we’ll have four columns to remove.”

Ease of operation and visibility were critical on the project. “The machines have push-button controls and great visibility. The tilt cab tips the whole cab back hydraulically. That makes it very nice to look up at your work and see what you’re doing,” Miller comments.

The machines feature full-length, hydraulically operated pins that pin the high-reach boom to the base boom. “Those hydraulic pins ensure that you get a good connection between the two booms,” Reeves asserts. “Because when you put a 6,600-lb. attachment up 90 ft. in the air, you want to have very tight connections. If you get slop in your joints, you will wave that tool around quite a bit.”

Reeves says the hydraulically extendable tracks on the high-reach machines give them very close to a square footprint. “They’re almost as wide as they are long,” he says. “That gives the machine excellent stability on the ground. The tracks widen and narrow down with the use of hydraulics in around 10 minutes. And yes, it’s a long-carriage machine.”

The Major Challenges

According to Miller, the biggest challenge of the Mulholland Bridge was to complete the demolition on time. But the crew faced other concerns, too.

“Obviously, safety on the job was a very important factor,” Miller states. “We had many safety meetings with the general and demolition contractors — before the demolition and during the work and throughout each shift. Everyone involved attended the safety meetings.” This included all of the field staff and project management personnel.

Fatigue was another challenge. “We were concerned about fatigue for the crew,” says Miller. “The guys were coming off a day job, or may even had that day off, but they were not really sleeping during the day. Then they needed to come to work at night.

“As far as visibility goes, the area was really well lit up,” he continues. “It almost looked like daytime working out there. The guys had a lot of adrenaline running out there beforehand. Everybody rose to the task and came through with flying colors.”

Before demolition, the work schedule had called for opening the bridge at 5:00 a.m. Monday morning. Bridge work on the roadway was completed some 16 hours ahead of schedule.