“There was a lot of preplanning on this job — I can’t stress that enough. You have to have it all right and you have the people trained so that when it starts going, it goes off correctly and there are no problems. One thing we’ve learned is that the system works only as well as the control.”
With this in mind, Combs suggested that the official surveyor on the project — Luis G. Riancho & Associates, Englewood, OH— set control points every 250 feet. “With those control points in that kind of proximity, we have checks and balances on either side of the machine as we go up the runway.”
Tom Gonzalez, 3D support technician with JC Equipment Sales, set up the PZL-1 and base station alongside the runway. Combs reported that some intermittent problems with radio signals led to his setting up the RE-S1 radio repeater. The system was consistently tracking 18 to 20 satellites, he said. During the previous day’s heavy rains, though, the windows on the PZL-1 kept getting wet, distorting the laser beam. With GNSS-only capability, Shawver decided to shut down operations.
But this was a new day. The cold planer was making two passes on each swath on the runway, first taking off 2½ inches, then a nominal 1½ inches. “The variable depth — that’s one advantage to having this system,” Shawver said. “It’s telling us what to cut and where to cut.” Avoiding overmilling would allow Barrett to minimize asphalt use when it came time to pave the milled areas, Shawver added. “Where we’re milling the concrete, we don’t want to have to come in and do a variable-depth asphalt lay. We just want to be able to do 2½ and an inch and a half to be at finish grade.”
The Millimeter GPS+ system passed its first test. Riancho verified the elevation of the milled surface on the first 1,000 feet of Runway 18-36 and the entire surface was within tolerance, except for one spot that was 4/100ths high. This was a much better scenario for Barrett than having overmilled. The motor grader also graded the blast pad within tolerances throughout.
“What we don’t want to have happen is for [Riancho] to come out and tell us that it’s wrong so that we have to tear it up,” said Meyer. “That impacts material costs, but the system also minimizes any mistakes that could occur, from stringlining to putting markings down.”
Besides the savings on materials, the system also provided savings in surveying costs. Combs pointed out that the cost of having a licensed surveyor constantly checking elevation and grade behind the cold planer would add up fast.