Construction Under Way on $482M Sixth Street Viaduct in LA

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Complex Highway Loop Benefits From Calculated Risk

Mon July 18, 2011 - West Edition
Jeff Winke


Once the old road surface’s 9 in. (22.8 cm) inches of concrete and a hot-sand asphalt subbase of 4 in. (10 cm) were removed, the trimmer was used to cut an additional 5 in. (12.7 cm) to achieve the new finished subgrade for the thicker pavement sect
Once the old road surface’s 9 in. (22.8 cm) inches of concrete and a hot-sand asphalt subbase of 4 in. (10 cm) were removed, the trimmer was used to cut an additional 5 in. (12.7 cm) to achieve the new finished subgrade for the thicker pavement sect
Once the old road surface’s 9 in. (22.8 cm) inches of concrete and a hot-sand asphalt subbase of 4 in. (10 cm) were removed, the trimmer was used to cut an additional 5 in. (12.7 cm) to achieve the new finished subgrade for the thicker pavement sect The Terex CMI TR-4503 trimmer uses two Trimble Smart GNSS antennae and a Trimble CB430 Control Box installed in the machine control station.

By Jeff Winke

SPECIAL TO CEG

There’s an old idiom that goes “What’s good for the goose is good for the gander,” which most folks take to mean that what’s good for one is good for another.

Rod Evans, office engineer/project manager of Sherwood Construction, Wichita, Kan., applied similar logic when looking at an expensive, once very valuable machine sitting idle in his equipment yard for several years.

“We’ve been using dual GPS machine control since late 2006 and understand the productivity edge the technology provides,” Evans said. “That got me thinking, why couldn’t the Trimble system work on the trimmer I have sitting here?”

He was referring to the Terex CMI TR-4503 trimmer-reclaimer that his company owns.

“We have a very large project where I wanted to try the concept out,” Evans said. “The Interdispersal Loop is a $70 million stimulus project involving the rebuilding of a major square-shaped highway loop around downtown Tulsa, Okla. There are interstate and highway interchanges at each of the corners and we’re working on three of the interchanges and all the paving in between.”

The Oklahoma Department of Transportation (ODOT) Interdispersal Loop project is massive. There are approximately 160 bridge deck spans that are being removed as part of this project.

“Our company’s job is to demolish all of the existing roadway and safety devices, and rebuild the subbase and base, and do all the concrete paving,” Evans said. “All the surfaces on the two sides of the interchange will be completely redone with new parapet barrier safety walls to replace old guardrails.”

Sherwood Construction is responsible for starting from scratch and then putting the network of roads, interchanges and bridges back together. Essentially, Sherwood completed all of the grading and paving, accommodating for elevation, grade and super-rotation throughout, while another contractor is completing the bridgework.

The trimmer was instrumental from the start. Once the old road surface’s 9 in. (22.8 cm) of concrete and a hot-sand asphalt subbase of 4 in. (10 cm) were removed, the trimmer was used to cut an additional 5 in. (12.7 cm) to achieve the new finished subgrade for the thicker pavement section. The materials coming off the machine were loaded onto a 60-ft. (18 m) conveyor belt that can be swung to either side, so that the dirt can be loaded right into a dump truck.

“We had equipped the trimmer with the Trimble GCS900 Grade Control System, which we had acquired from Foley Equipment. This meant it could run off the 3D digital model. This ensured incredible accuracy and consistency as it trimmed through all the superelevation-rotations in the curves,” Evans said. “As far as I know, we are the first contractor to try a dual-mast GPS system on a trimmer — and, I’m happy to say that it works just as I thought it would.”

When the Trimble field engineer first arrived to do the system install on the trimmer, he was expecting a single antenna mast that would work off a robotic total station. The technician was surprised to see that Evans had installed mounting bases for two masts, one on each side of the machine, in relation to the cutting edge. It was to be set up like a motorgrader.

“My logic was that if the Trimble GPS system works on a blade, it’ll work on either end of this trimmer head,” said Evans. “It functions the same controlling hydraulics to raise, lower, and tilt a cutting blade — I was just sure that it would work.”

The trimmer uses two Trimble Smart GNSS antennae and a Trimble CB430 control box installed in the machine control station.

“I admit, we were kind of working in the dark as to whether this would work,” Evans said. “Our local dealer, Foley Equipment, and Trimble installed the system on the trimmer; tested it in our yard for a couple of days; and it worked just like I thought.”

The Terex CMI TR-4503 trimmer-reclaimer equipped with the Trimble GCS900 is achieving finish grade within a quarter inch to three-eighths inch. (.6 to .9 cm)

Accuracy requirements on the Tulsa Interdispersal Loop project are tight given the density of bridges and complex geometrics.

Including the trimmer, Sherwood Construction has 13 GPS-enabled machines. The company achieves all of its own initial surveying and confirmation of grade accuracy through its four survey crews each equipped with a R8 Trimble GPS system and S6 Trimble robotic total station. The S6 robotic total station is accurate to one arc second in the vertical and horizontal angles, making it ideal for the Tulsa project.

“That’s really my job—making sure all this paving, every edge, every elevation that is provided to the field is accurate,” Evans said. “It is a lot of work. We had some 7am to midnight days for about 30 days because we had to wait until they got the bridge decks off, and then we had to fit all the alignments and vertical control—what we call the hunch grades—to make sure the bridge approach matches up with the bridges.”

Sherwood hustled because the firm faced $20,000 a day liquidated damages.

Considering the massive size of the project, the excavation was pretty modest.

“There’s approximately 13,800 cu. yds. of excavation, which isn’t that much,” said Evans. “We were lowering this pavement four or five inches.”

There is approximately 100,000 sq. yds. (83,612 sq m) of concrete pavement over the whole project, which includes approximately 160 bridge decks that will be removed and replaced. The bridge spans are anywhere from 80- to 100-ft. (24 to 30.5 m) in size. Most of these bridges were challenging because of the complex alignment geometry and unique super elevation rotations.

Additionally, there is 20,000 to 25,000 linear ft. (6,096 to 7,620 m) of high-depth parapet wall, which is the concrete barrier wall that will be seen along the road.

“The trimmer is enabling us to achieve incredible accuracy,” Evans said. “We’re checking with a robotic total station and it’s confirming that the trimmer is cutting grade with one pass. Without the Trimble system you may have to make two or three passes.”

Evans knows that the finished paved surface will be accurate and smooth.

“When paving is applied to this surface it’s going on top of a surface that’s already been generated by a precision 3D model and the trimmer has finished to these specs rather than finishing between blue tops that are set 50-foot apart. We’re just getting a lot better results and a lot better results with minimal to no yield loss on the concrete.”

Considering the challenges that Sherwood Construction faced on this complex project Evan concludes: “When we had removed the old roads and bridge surfaces, our biggest concern was the question ’how are we going to put this back together geometrically?’ We had to accomplish everything within demanding parameters that call for redesigning and reestablishing all these grades on new elevations, and everything had to be completed within deadlines that accommodate three demo crews, two subgrade prep crews, four bridge crews and a paving crew. This is an arduous task that we were able to accomplish with some intelligent risk taking, like using the Trimble dual GPS system on the trimmer.”