Hitting the Soil on the Head

Case Studies
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Even for good construction crews like Dawn Watson’s, staying on schedule while maintaining project specifications can be challenging. The crew, employed by Walsh Construction, was recently tested on the rebuild and widening of a three-and-a-half-mile segment of Tri-State Tollway I-294 outside Chicago.

Knowing it would need reliable compaction equipment for the project, Walsh tested BOMAG’s BW213DH-4 BVC single-drum vibratory roller, featuring Intelligent Compaction technology that has the “smarts” to know when compaction has reached an optimal level.

The roller’s Terrameter system measures stiffness of compacted soil by monitoring the relationship between the soil contact force and deflection of the roller’s drum. Terrameter also identifies areas that have and have not achieved optimum compaction.

BOMAG’s Variocontrol system uses Terrameter’s information to automatically adjust the drum’s output energy. A “vectoring” process manipulates the drum angle to produce glancing blows where higher density has been achieved, and direct blows where soft spots exist. Both over-compaction and under-compaction are avoided, and all readings are documented.

Material densities were previously judged only by experience while a testing device analyzed the results. With Intelligent Compaction, Watson’s crew has complete confidence that correct density is achieved – every time and throughout the area being compacted. The crew can then move forward on a project, rather than waiting for go-ahead from quality control personnel monitoring job progress and compaction levels.

“The roller always gets us to the density we need,” said Watson. “We can trust the information from the machine. QC people come out to test and it passes every time.”

On the Tollway, Walsh is using CA6 crushed limestone as sub base, calling for 100% density. “It’s even more challenging when you have to be perfect,” said Watson. “We know the roller will get 100% density without concerns about over- or under-compaction.”

The BW213DH-4 BVC also assisted another Walsh crew on the Tollway. “They had issues achieving density because the rollers couldn’t produce enough force,” said Watson. “After three passes with the 213 it was done. So we opted to purchase a second unit.”

The roller delivers 82,125 lb of centrifugal force, 22% more than BOMAG’s same size standard model roller. “I was worried initially that we were going to pulverize the aggregate,” said Watson.

“But the machine is smart and eases off as it achieves compaction. The 213 makes two or three passes, compared with five or six with a regular roller. It cuts the time in half.”

According to Watson, the roller compacts 5,000 tons of material in a 10-hour day. “That’s not a hard push day,” said Watson. “We’re using it 70 to 80 hours a week.”

The roller hasn’t yet been tied in with GPS to provide exact coordinates for compaction results, but it’s the step Watson would like to take next. “It would be phenomenal to get results 100% proven,” said Watson. “It would free up time we spend dealing with the DOT and allow us to move along at a much faster pace.”

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