Dawn Watson’s excavation crew worked hard to stay on schedule and maintain the required project specifications on the rebuild and widening of a 3.5-mi. segment of Tri-State Tollway I-294 in East Hazel Crest, Ill.
Watson, a job superintendent who has worked for Walsh Construction since 1998, had her crew begin work in March 2005 on the Tri-State Tollway I-294, which ran through the Southland Corridor on the outskirts of Chicago. Completed in October 2006, the job took up a $140-million chunk of a massive $5.3-billion undertaking by the Illinois Tollway to implement motorist-friendly open road tolling.
Walsh Construction, a company that performs construction services in 36 states and operates out of five regional offices across the country, employed Watson’s team.
Debuted Nov. 2005, the toll system allowed users of a special I-PASS to avoid time wasted by stopping at toll plazas.
Instead, commuters’ tolls are electronically recorded through transponders in their vehicles as they pass by each plaza at highway speed.
Among the intended goals of the overall plan was reduced traffic congestion and shorter commute times. While the overall success of the new tolling enterprise was out of Walsh Construction’s control, the company played a key role in the quality of the new roadways from the ground up.
Walsh’s preconstruction preparation made the work run smoothly on the I-294 job, which called for an expansion from six lanes of traffic to eight, as well as the installation of retaining walls and a few bridges, good planning was essential. Part of that planning involved having reliable compaction equipment at the site.
Watson had asked her crew about a third of the way into the project to try out a new roller provided by West Side Tractor Sales Co., an equipment dealer based in Naperville, Ill. While Walsh’s other rollers had been reliable for the crew, the company tested the new machine, a BW213DH-4 BVC single-drum vibratory roller from Bomag.
The BW213DH-4 BVC is one of the new wave of Intelligent Compaction rollers that are starting to make an impact in the North American market. The technology built into the machine has the “smarts” to know when material compaction has reached an optimal level.
A standard feature on the new roller is Terrameter, which directly measures the stiffness of the compacted soil by monitoring the relationship between the soil contact force and the deflection of the roller’s drum. Terrameter also has the ability to identify the areas that have and have not achieved optimum compaction.
Bomag’s Variocontrol system takes the roller to the next level by using the information from Terrameter to automatically adjust the output energy of the drum. This is accomplished through a “vectoring” process that manipulates the angle of the drum’s energy to produce glancing blows where higher density has already been achieved, and direct blows to the material where soft spots exist. Essentially, both over-compaction and under-compaction are avoided and all readings are recorded and documented throughout the compaction process. Previously, a roller operator’s ability to judge material densities, experience and the use of a testing device to analyze the results were the only methods.
With Intelligent Compaction automatically determining material stiffness, Watson’s crew had complete confidence that the correct compaction density had been achieved throughout the area being compacted. This enabled the crew to move to the next section of a project, rather than first waiting for a go-ahead from quality control personnel who are constantly monitoring job progress and compaction levels.
“The roller always gets us to the density we need,” said Watson. “But, more importantly, we can trust the information the machine is giving us. Every time my operator has told me that the roller says we’re finished compacting a given area, it’s been right. So once I get the word, I move the machine right out and onto other business. The QC people will come out the next day to test and it passes every time.”
Depending on the location, scope of the project and material being used, various agencies have different requirements for road base compaction. On the Tollway project, Walsh Construction had used CA6 crushed limestone as subbase material, which called for 100-percent density.
“The job is always challenging, but it’s even more so when you have to be perfect,” said Watson. “We can rely on the roller to get 100-percent density without any concerns about over- or under-compaction. That’s definitely a lot of stress off me.”
As helpful as the intelligence aspect of the BW213DH-4 BVC had been, it was not the initial factor in the decision to buy the machine. The purchase actually came about when another Walsh crew had difficulty achieving enough material density on a separate portion of the Tollway project.
“We have a brother job going on up the road at the Cermak Road toll plaza where they had some issues getting compaction densities because their rollers couldn’t produce enough force,” said Watson. “We sent the 213 over to see if it would solve the problem, and after three or four passes it was a done deal. Right after that we bought another unit from West Side so each crew could have this machine. It hits much harder than a standard roller, so it definitely was the tool for the job.”
The BW213DH-4 BVC delivered 82,125 lbs. of centrifugal force, a 22-percent increase over BOMAG’s standard model roller of the same size. More available force translated into faster compaction and subsequently, less time needed to complete the job.
“With that amount of force I was worried initially that we were going to pulverize the aggregate,” said Watson. “But the machine is smart, and it eases off as it’s achieving compaction. When we’re dealing with material that has the proper moisture content, we get compaction with the 213 in two or three passes, compared with five or six with a regular roller. It basically cuts the work time in half, and because of the automatic adjustments the machine makes, it seems like it’s much easier on the material as well.”
The increased production gained from the new roller has been extremely beneficial for Walsh. Watson estimated that the machine compacts about 5,000 tons of material in a 10-hour day.
“And that’s not a hard push day,” said Watson. “We’re putting between 70 and 80 hours a week on it. We’ve really gained some great use from the roller. We even used it in some deep, wide trenches to compact a dirt bed over pipe that we laid.”
Watson said that the roller had not been tied in with GPS to provide exact coordinates for their compaction results, but it was the step she’d like to take next.
“We run GPS with our dozers, and it’s only a matter of time before we do it with the roller,” said Watson. “It would be phenomenal to get our results 100-percent backed up and proven, because it would free up so much of the time we spend dealing with the DOT. Basically it will just allow us to keep everything moving along at a much faster pace.”
With more jobs on the Tollway upcoming, Walsh Construction will continue to use the technology of the BW213DH-4 BVC.
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