Dredged with Accuracy For the Grassy Point job, Veit used two Liebherr excavators with clam - shell buckets on barge spreads. Each was equipped with the Trimble Earthworks Grade Control Platform using the Minnesota Department of Transportations’ MnCORS VRS Virtual reference station network for instant access to RTK positioning services. “One machine would excavate to design and load the material. Two tugboats moving four hopper barges were used to transport the material to the placement site. The other unit would unload the material, placing it on the seabed to a design grade. This was all achieved with Trimble guidance,” Lawson said. “We also had a Trimble Siteworks Positioning System with a TSC7 Controller that was performing quality control/ quality assurance checks behind both spreads.” The Veit team relied on a remote connectivity cloud platform to remotely manage the units. Bi-weekly as-built progress surveys were completed by survey crews using a single beam sonar. The subsequent surveys were then uploaded to the machines for reference. “The data from the single beam echo sounder was compiled in Trimble Business Center and sent out with plan sheets,” said Lawson. “We used aerial drones to gather topographic data of the island surface above the water and then combined those surveys with the machine mapping data. That process helped significantly to reduce rework. We never had to go back because it was field-verified right away.” The Trimble Marine Construction System makes the process much faster and more accurate. Lawson estimates that the initial excavation is about 50 percent quicker than traditional methods because operators know where the bucket has been and where it needs to go. Lawson added, “With the 3D visualization, we have greater assurance that cut depths are accurate as compared to a mark on the stick. Reducing the time spent returning to a site for rework is invaluable.” Enabled by technology, Veit crews worked 24-hours a day, Monday- Saturday, to complete the required tasks from June to September 2020. Summer 2021 will conclude the restoration project, finishing the cap on the Grassy Point islands using clean sediment removed from Kingsbury Bay, dredging remaining excess sediment from open water
portions of Kingsbury Bay, restoring Grassy Point wood removal ar - eas using sediment from Kingsbury Bay and restoring and reseeding disturbed areas. Lawson concluded, “I cannot imagine performing this project with - out 3D positioning technology. Using the Trimble workflow greatly contributed to our success and reduced our rework to almost none. We would not want to tackle this type of project without the 3D tools we had available to us from Trimble.”
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DECEMBER 2021 csengineermag.com
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