Engineering Inc. - November/December 2007 - (Page 38) guest column technology StakeleSS earthwork: time and CoSt SavingS in Stream reStoration By Brad Fairley For construction projects, the old adage “measure twice, cut once” isn’t just an expression—it’s crucial. A small surveying mistake could delay a project for weeks or even months, not to mention cost hundreds of thousands of dollars to repair. So what if you could reduce or eliminate the need for construction stakeout? Thanks to the wonders of modern technology, you can. Computer-aided design makes it possible to prepare 3D designs for construction sites. When coupled with GPS-guided construction equipment, a 3D design allows contractors to monitor their work and graphically see how it compares to the design from the cab of their equipment— all without any construction stakeout. This 3D technique, common in roadway design and construction, is proving its worth for new uses, too, such as stream restoration. Stream restoration involves restoring the dimension, pattern and profile of a degraded stream system, which generally entails excavating a sinuous channel with a changing shape and installing in-stream grade control structures. Tolerances on slope, channel cross-sectional area and elevation of the structures are extremely narrow. Stantec, Inc., recently demonstrated the advantages of using 3D technology for a Brad Fairley stream restoration project in Columbus County, N.C. Working with the North Carolina Ecosystem Enhancement Program, we first designed and constructed more than 1,000 feet of stream channel using traditional 2D design and construction stakeout. To test the 3D process, we also designed a portion of the site in 3D and outfitted the contractor’s backhoe with a global positioning system (GPS). The GPS enabled the equipment operator to observe, through horizontal and vertical control, how closely the excavation matched the design and adjust accordingly—all without additional staking or redundant field measurement checks. “Normally, stream restoration construction is an iterative process,” said Dave Bidelspach, lead designer of Stantec’s Environmental Management Group in Raleigh, N.C. “First the contractor has the site staked. Then excavation begins. With the complicated earthwork and tight elevation toler38 engIneeRIng Inc. novembeR / DecembeR 2007 ances, the contractor then has to repeatedly stop, check elevation and location and make adjustments. This 3D technology greatly speeds up the process since the backhoe operator can see how his excavation matches up with the design on a screen in the cab of his backhoe.” After completing the remaining 1,000 feet of the project with the aid of 3D technology, the contractor estimated that construction proceeded at a rate of 20 percent to 30 percent faster than conventional methods. Time is a major construction cost for stream restoration projects; saving time typically results in saving money. It’s projects such as this one that validate what many engineers and contractors have already begun to understand—while surveying is still a necessary step in the design and construction process, it continues to change shape as technology evolves. In reality, 3D designs and stakeless earthwork can hold a number of advantages over traditional methods. Where stream projects are concerned, the use of 3D design techniques and tools can all but eliminate construction stakeout, speed the construction process and assist in the preparation of “as-builts.” The result is an efficient construction process that saves both time and money. Stantec’s Environmental Management Group continues to design its stream restoration projects in 3D and encourages contractors to use GPS-guided construction equipment to reap the maximum benefit from the design. Stantec continues to explore the opportunities that 3D technologies hold for future stream restoration projects. One day soon, it might be possible to upload 3D designs to the construction equipment via e-mail. That way, the contractor could immediately contact the designer about a problem (e.g., bedrock) and the designer could e-mail the revised design directly to the equipment in a matter of hours. Given the strides we are making with current technologies, such realities are undoubtedly not far off. n Brad Fairley is a managing senior associate for Stantec, Inc., a Raleigh, N.C.–based design and consulting company.
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