A step ahead: Leveling with Wirtgen’s large cold milling machines
With the W 210i, three selectable engine speeds enable complete pavement removal at a full depth of 13 in. However, at OAK, the milling depths varied constantly. “Cutting to the digital models, and staying within the confines of all the different models, was one of the biggest challenges of this job,” Eddy said. To achieve optimum milling results, Wirtgen cold milling machines offer state-of-the-art features. These include one of Wirtgen’s core technologies – leveling. When the surface course is removed, the LEVEL PRO leveling system continually compares the actual milling depth with the preset target milling depth. LEVEL PRO can work with different sensors – cable, hydraulic cylinder, sonic and slope sensors or laser and sonic ski sensors as well as multiplex systems – and can be extended as required. 3D leveling is also possible with installed interfaces that are compatible with 3D systems from common manufacturers.
The digital terrain model presents challenges
So the total station system interfaced seamlessly with Wirtgen’s LEVEL PRO system, which converted the signal to Wirtgen’s ’language’ and “made the appropriate grade changes based on the currently required elevation,” Eddy said. Accuracy of milling was within hundredths of a foot. “The speed and the depth varied so much, as we went from cutting zero in some areas, to 11 in. in other areas, depending on what the digital models required,” added Graves. In fact, there were five different models for the W 210i cold milling machines to work with. “There were benches of pavement remaining everywhere, at all different sizes, shapes and depths,” explained Eddy. “Areas of distressed pavement were identified prior to the milling operation, and they were built into the digital models,” Graves continued. “There was a minimum requirement of asphalt to be removed for each. The asphalt was to be milled out at 3 in. increments, so if we had to cut 8 in. we had to go 9 in. deep.”