By Mark Rea

Three-dimensional technology and global satellite positioning are much more than science fiction to today's highway and heavy contractors in Texas.

Name any of the state's largest highway projects currently under construction and chances are good that at least one of the cutting-edge technology systems is being used on them.

Global positioning systems, more commonly referred to as GPS, began several years ago as a military weapon to help pinpoint potential targets. Recently, the systems have been marketed to outdoor enthusiasts such as fishermen and hunters.

In the last few years, contracting firms that specialize in highway and other heavy projects have found use for the systems in surveying of sites and as they make grading cuts.

"It is the most accurate instrument that is currently in use for survey," said David Owen, vice president of Dallas-based GeoShack, which markets the technology throughout North and Central Texas. "It makes the process easier, quicker and much more accurate because most of the errors occur in surveying during communication between the two people manning the total station. This eliminates the two-man crew and totally automates it."

For many years, the total station instrument that requires two people to analyze data from two specific points on the ground performed site survey. With a prism pole on one end and a rod on the other, measurements were taken by backsiding specific points and their relative positions on the site.

With the new technology, the traditional two-person crew with the distinctive yellow tripods is replaced because the grading equipment operator can access immediate data on 3D readouts inside the cab of the machinery, making adjustments on the fly.

Brian Salerno, project manager for San Antonio-based Zachry Construction Corp., is using a trio of GPS survey machines on the Dallas High Five project, a $260 million project that is one of the most ambitious ever undertaken by the Texas Department of Transportation.

"What we like about these systems is that we believe they have allowed us to do more work with less survey crews out on the project, and it provides us with a lot quicker access to the survey information," Salerno said.

He added that the systems also promote safety because "any time you can cut back on the number of people out there working, that means less people who can potentially suffer an injury."

Robotic, GPS Technology

Two different types of technology are currently available to contractors.

The first is based upon a robotic total station, which is utilized to track a prism mounted on the machine. It utilizes the positional data of a total station and compares it to a digital model of the job, and adjusts the blade height based upon that data.

"In other words, it makes changes automatically," Owen said. "Anywhere the machine operator goes on that job, he will achieve the proper grade to one-200th of a foot, or approximately one-eighth of an inch."

The robotic total station has the technology built into the instrument. With a traditional total station, someone has to actually stand behind the instrument, look through the scope, find the prism and physically point at a second crewmember manning the rod.
The robot can track that prism automatically, so whenever the prism moves, the data changes and the blade position adjusts accordingly.

Robotic total systems also utilize a larger prism system than a pole system, and since it is part of the earthmoving machinery, the machine itself acts as the survey pole. With different sensors and measurements, the technology can make calculations from the prism and transmit the information to the tip of the blade for accurate positioning.

There is a display monitor in the cab and the operator has a variety of information available. He can choose from a plan view, where he can see a top view of where he is on the job-site at any time, or a cross-section view, where he can see the plain of the road and reference his particular point on the site. Text information such as site coordinates, stationing, elevation of the blade and what the desired elevation of the blade needs to be is also available to the operator.

"Everything he needs to know about the elevation of that blade is available to him either in a graphic or in text form," said GeoShack 3D specialist Mark Purselley. "That information is displayed for the operator right there, so he never has to leave the cab."

The other type of 3D technology relies upon GPS, which utilizes an antenna on the machine rather than a prism to receive positional information from satellites. The advantages are elimination of the line-of-sight requirement.

"All you need is to be able to see the sky," Owen said. "That isn't much of a problem on a construction site."

With GPS, a reference station is installed over a known point on the site, but the machinery can work 6 to 8 mi. away.

"While the robotic station must be set up every day, with GPS, you simply turn the system on and go to work," Owen said.

The accuracy of the GPS system is only one-tenth of a foot, or just a little over an inch. "We call it a rough-grade system, but it's perfect for subgrades," Purselley said. "A lot of jobs are built with the one-tenth accuracy, so the bulk of the work can be done by GPS. Then the robot is utilized for the fine grading system to finish the project."

Three of the major companies that currently manufacture the robotic total stations include Sunnyvale, Calif.-based Trimble, Paramus, N.J.-based Topcon America Corp., a subsidiary of Japanese-owned Topcon Corp., and Switzerland-based Leica Geosystems AG.

Growing Popularity

Popularity of the survey technology is steadily increasing throughout Texas. Zachry Construction is utilizing several pieces of the equipment on the High Five project and is also employing the technology at Interstate 35 in DeSoto and State Highway 151 in San Antonio.

Other state contractors using the equipment include Dallas-based Austin Bridge & Road, Jones Bros. Dirt & Paving Contractors Inc. in Odessa, Arlington-based Archer-Western Contractors Ltd., Weir Bros. Inc. of Dallas, Champagne-Webber Inc. of Houston and Fort Worth-based Gilbert Texas Construction LP.

Gilbert Texas is currently employing 3D technology on its IH-30 project in Dallas and the GPS system on the U.S. 287 project in Hardeman County near Chillicothe.

"We get a lot higher production with these instruments, especially when we are putting in the flex base material," said Shea Huckaby, district survey manager for Gilbert Texas. "There is no staking and no guesswork as to where it's going to go."

Meanwhile, Archer-Western is the contractor for the SH 183-A project in Austin, and Purselley said it was bid with the 3D technology in mind. "The SH 130 project in Austin has been designed similarly with an initial investment of nine systems, and the Loop 1 project there is also being designed with the 3D system," he added. "Contractors are front-loading the jobs with the systems to save themselves on time and money."

The technology is not inexpensive, costing about $100,000 for each machine, but it is proving to be worth the investment.

"I think it correlates to reduced labor and the actual putting of the survey stakes into place," Salerno said. "As a result, despite the cost of these machines, they are actually cost-effective. They pay off in the long run."

In addition to use on motor graders and dozers, a prototype milling machine, owned and operated by G.T. Sirozzotti Excavating of San Antonio, is utilizing the technology on the SH 151 project in the Alamo City. Rather than being able to mill only on a flat plain, the machine allows milling to be achieved along the normal 2 percent slope that serves as the crown of most roadways from the middle to the shoulder.

"The technology is built right into the system to give the operator the information needed to manipulate the machine accordingly," Purselley said. "It's fully automated so that the operator merely steers the machine and the system makes the adjustments."

Salerno said Zachry Construction has "grown up" with the new technology.

"We started with the older systems that had the spinning laser beams that would give a look at where you were for cut or fill," he added. "Since then, we have progressed through the robotic controls on the survey instruments to machine control and now the GPS control. It's obvious to us that these machines help us do what we need to do more efficiently than ever before."