GPS: It’s Not Just for Grading Anymore
At a Phoenix commercial/industrial development site, GNSS equipment wears a number of hats.
The sign of a great technology is not how much of an immediate impact it has on an operation or an industry, but rather how it matures in use over time. With that as criteria, it would seem that GNSS is truly hitting its stride. Its far-reaching impact has been evident in a major Tempe, Arizona, site clearing and development project, where Buesing Corp. is using GPS for a number of varied processes onsite.
A lot in the past
The project in which Buesing is currently involved as a subcontractor to Ryan Companies, a $650 million development called Marina Heights, will feature almost 2.1 million square feet of combination office and retail space.
“The site design includes a below-ground podium parking garage for more than 8,500 cars,” said Buesing project engineer, Dan Kuehl. “When we first arrived onsite, we removed all the asphalt from the site’s previous use as a lot, had it ground down and sold it as RAP to a local asphalt company. The earthmoving effort itself included removal of more than 425,000 cubic yards of material.”
Drilling for stability
Because of the general soil composition and the site’s proximity to the Salt River, precautions were taken to ensure soil stability throughout construction. This meant, among other things, installation of nearly 1,400 24-inch diameter column shafts, drilled, then injected with a concrete slurry mixture. Getting to a point where they could effectively drill for those shafts involved some additional work and brought their GPS capability onto play, said Kuehl.
“To install the column shafts in advance of the shoring wall we decided to construct several temporary benches — of varied heights — off which the drilling and support machinery could work,” he said. “But because survey on the project was being handled by the developer, none of those temporary benches existed on any of the original plans.”
Buesing addressed that issue by modifying the existing 3D model then, using a Cat 140M motor grader with Topcon 3D-MC GPS machine control (purchased through the Gilbert, Arizona office of Branco Machinery), constructed each of the benches. To conduct daily grade control and meet the tight tolerances needed for the shoring wall line, Kuehl and his crew used their own Topcon GR-5 base and rover full time as supplemental survey.
"GPS has been a huge part of our success."
The Marina Heights project design includes five separate structures, each with a unique subgrade elevation. Originally, a single master GPS model provided guidance and verification to crews involved in the mass excavation. According to Kuehl, however, Buesing opted to generate additional models better suited to the functions they are self-performing.
“We created a secondary model of the mass excavation plan for this entire site,” he said. “That helps us not only for layout with our base and rover, but also for use of the 140M motor grader, one of our Cat 374D excavators and probably even our dozer. We are a GPS company — we have been for some time — it just makes sense to capitalize on that.”
Because formal surveying is already being provided, one would think the Buesing’s dependence on GPS would be lessened. However, Brett Smith, another project engineer at the Marina Heights site, said that the technology has become so second nature to them that to proceed without it is almost unthinkable.
“On nearly 80 percent of our projects, we handle our own survey,” he said. “We were able to do the benches because we knew what we wanted and how to get there. I simply sat down with Dan for an hour, we built the GPS model, output it for use with the Topcon 3D-MC GPS and suddenly we were building benches that were not in the plan.”
Buesing is also capitalizing on GPS’ ability to help with volume calculations, an area that had long been a tedious and time-consuming effort. Today, using that GNSS capability, Smith said they are able to quickly and easily perform those tasks to, among other things, generate quantity estimates.
“Another good example of this can be seen in ‘turnover areas,’ sections which have firm milestone dates at which work must be completed. Doing that is now as simple as taking a quick topo and comparing it to our model. If we see that we have 60,000 yards remaining and 15 days to move it, we know we have to move 4,000 yards a day. From a planning standpoint, that can be huge. We even used our Topcon rover to verify elevations for the nearly 4,000 soil nails and tiebacks as part of an as-built effort for our records.
“This is a complex project with a lot of intricacies in the grading, the shoring, and so on. But it’s been great right from the outset and I know a lot of that is because we’ve maximized use of the technology we have. GPS has been a huge part of our success.”