Transportation, Environmental Needs Meet Halfway
A Deere 850J dozer equipped with a Topcon PG-A3 rover antenna and in-cab 9168 control box and monitor grades the site of a large holding pond that is part of a wetlands remediation project accompanying a new interchange at I-5 in southwestern Washington. Don Talend photo.
When you drive up to southwestern Washington state from Portland, OR, on Interstate 205 to I-5, it doesn’t take long to notice an uneasy coexistence between Pacific Northwest residents’ need to get around and the political will for environmental preservation. Bicyclists accompany vehicular traffic on a bike path between the northbound and southbound vehicular lanes on I-205. Farther north, the highway cuts through a noticeably rural region accented by rolling terrain and tall pines, with no scarcity of traffic between Portland and Seattle.
Just a few miles north of the Columbia River, which separates Oregon and Washington, the Washington State Department of Transportation is addressing growth in the area – and the higher traffic volume sure to follow – by improving access to I-5 from towns that are evolving from rural communities to true suburbs. In the process, the state is going to great lengths to preserve the project’s surroundings.
In 2001, WSDOT completed a two-year study of the I-5/I-205 interstate corridor. As part of the study, the department identified the short- and long-term interstate and interchange needs in the north Clark County area. Ultimately, a new I-5 interchange near northeast 219th Street (State Route 502) was planned to open to vehicular traffic by October 2008 with full completion by spring 2009 at an estimated cost of $56.1 million. The project is being financed by a state Nickel Funding Package, which is funding 158 projects over a 10-year period and includes a 5-cents-per gallon gas tax increase, a 15-percent increase in gross weight fees on heavy trucks and 0.3-percent increase in the sales tax on motor vehicles.
Part of a larger regional growth spurt, the area near the city of Battle Ground, WA, is booming, and increased traffic volume proves it. WSDOT’s study indicated that the Vancouver/Portland area’s population grew by more than 153,000 between 1980 and 2000. Further, the area’s population is forecast to grow by slightly less than 540,000 by 2025, a population growth of 63 percent from 2000, and employment will grow by 68 percent during the same period. With little or no fixed-route transit service in the area, according to the study, vehicle miles traveled are expected to increase by as much as 70 percent, while I-5 and I-205 between Vancouver and Portland will see a 50-percent increase in vehicle trips.
In February 2007, WSDOT awarded Kerr Contractors Inc. of Woodburn, OR, a contract to build the new interchange, and work began that spring. In addition to pavement for the ramps and an extension of SR 502 east of I-5, a 720-foot-long bridge over I-5 was being constructed to carry an eastbound and a westbound lane of traffic to and from the interstate. Prior to completion, drivers had to head south on 10th Avenue, which runs parallel to the interstate to the west, and access I-5 from northeast 179th Street.
As of midsummer 2008, the final structural component of the bridge structure had been constructed, and crews were continuing to work on the pavement, bridge structure, bridge approach slabs, and traffic barriers. Construction was on schedule despite major storms and flooding in December 2007 that caused a six-week delay. While this work was going on, Kerr was also mitigating the environmental impact of the project immediately to the east of 10th Avenue with the help of the latest grade-control technology.
Remediating Wetlands – Efficiently
East of I-5 is a major environmental component of the project: remediation of nearby federally protected wetlands. Kerr’s work on a 42-acre site included 12 acres of wetland creation, 5 acres of wetland enhancement and 17 acres of wetland buffer construction. In the process, Kerr excavated 131,000 cubic yards of material, including 49,000 of cut and fill and another 82,000 hauled off and used to construct berms around the ramps.
Kerr used technology for grading the site that dramatically increased its productivity: a Topcon Positioning Systems Real-Time Kinetic (RTK) Global Navigation Satellite System (GNSS) that the company purchased from The PPI Group, a dealer of surveying and construction equipment with several operations in the Northwest, including Portland and Seattle. The contractor is ahead of most of the rest of the construction industry, having used the technology since 2002 for grading projects such as roadway subgrades and a 100-acre shopping mall.
GNSS technology is beginning to make a major impact on excavating and surveying. Increasingly, contractors like Kerr are implementing machine control systems on earthmoving, grading and paving equipment such as scrapers, dozers and motor graders, plus milling machines and asphalt and concrete pavers. A GNSS survey system uses a "rover": a rugged antenna mounted to a shock-absorbing, vibration-damping pole and a receiver box mounted in a secure location on the machine. Satellites send positioning data to another antenna/receiver combination at a stationary base station. Positioning data is also sent to the rover on the machine. The stationary base and mobile rover work together to provide RTK position information, revealing the machine’s three-dimensional location on the site.
Software compares the machine’s position to the design grade at a given location. The design grade information was compiled via the use of the GNSS – including "roving" of the site. The data files are loaded into a machine-mounted control box via a compact "flash card." The control box updates positioning data and sends signals to the hydraulic valves. The blade is automatically positioned for elevation and slope. Other sensors inform the control box of certain machine conditions; for example, dozers used by contractors such as Kerr are equipped with a slope (tilt) sensor on the blade to measure the cross-slope of the cutting edge. "Indicate systems" like Topcon’s 3-D systems provide visual guidance for machine operators, who manually control the machine to cut or fill to the desired grade.
"Contractors such as Kerr are taking advantage of huge leaps in productivity, improved accuracy and material savings that GNSS provides in terms of both grading control and surveying," says Jeff Peterson, senior vice president of The PPI Group. "Because they don’t need to devote manpower to grade staking a site, the machine operator can prepare a site single-handedly and also hit the ground running at the start of a shift, and the operator and grade checkers know at all times exactly where they are to design grade. On the sales side, this increased productivity allows the contractor to complete a project in fewer days and move on to another project, which helps them to improve their bottom line and grow their business."
It’s late July 2008 and with the Topcon HiPer Lite + base station deployed near the road and visible in the distance, a Deere 850J dozer equipped with a Topcon PG-A3 rover antenna and in-cab 9168 control box and monitor cuts a long swath of dirt with several passes. While driving forward, the operator looks at the monitor, which indicates the need for him to raise or lower the blade.
Meanwhile, Josh Vanderzanden, site foreman, scans the site. Two large stormwater holding ponds will be excavated on the north end and separated by flow-control structures. Working in conjunction with another much larger one located on the south end of the site, these holding ponds will include flow level control structures that will gradually release stormwater to a sloped geogrid area covered with tree cuttings. The stormwater will flow across the tree cuttings – which will impart bacterial action to the water, the way a natural wetland would – and eventually make its way to nearby Gee Creek. "What we try to do is make these wetlands that we’re building here as natural as possible, so we use trimmings and cuttings from trees to build the geogrid area so that it can be as close as possible to what Mother Nature intended it to be," says Vanderzanden.
In addition to stormwater management, the site is also making allowances for wildlife. Vanderzanden points out that several trees felled for construction of the ramps will be trucked over to the wetland remediation area and laid on the ground. Kerr will also make brush piles and plant more trees on the site which, along with the felled trees, will create wildlife habitat.
The accuracy of the system is making the site preparation work much more productive, says Brent Kerr, president of Kerr Contractors. "Trying to run a stringline and stakes on something that’s not a constant grade – that’s a lot of work, a lot of layout, a lot of updates. [The GNSS] makes grading so much more precise," he says.
The site’s close adherence to the topographical survey was demonstrated when a WSDOT inspector recently stopped by with his own GNSS equipment and "roved" the site to determine how closely within specification the grading is.
"He compared his readings with what I look at in the dozer and it’s absolutely ‘dead-nut’ – to the hundredths," adds Vanderzanden. "I was waiting for that for two weeks."
The accuracy of the system allows Kerr to make a major leap in productivity. The company estimates that the system increases grading productivity by about 20 to 40 percent.
"Typically, you always have to be thinking you’re prepping an area and you’ve got surveyors coming in," notes Vanderzanden. "This way, you can start in the back and work to the front, and you don’t ever have to worry about stepping on anybody else’s toes. It speeds up your process. It would be hard to come up with a number, but it’s substantial."
Kerr is using another GNSS unit, a HiPer Lite + rover, to check grade during construction of a bioswale that runs parallel to the northbound I-5 shoulder. Greg Dandurand, surveyor for Kerr, holds the unit and conveys readings to the operator of a Caterpillar D5G dozer, who grades and compacts the slope facing the highway. The rover is working in conjunction with a second base station, set up on high ground near the southbound off-ramp west of I-5.
Here and along the SR 502 extension to the overpass, bioswales are being constructed and lined with a WSDOT-specified Ecology Mix – a pervious, alkalinity-generating media consisting of dolomite, perlite and gypsum. The mix is designed to remove suspended solids and soluble metals from highway runoff through physical straining, ion exchange, carbonate precipitation, and biofiltration. Dolomite and gypsum add alkalinity and ion exchange capacity to promote the precipitation and exchange of heavy metals for light metals as well as precipitation of phosphorus. Perlite improves moisture retention, which facilitates the formation of a biomass of epilithic biofilm.
Dandurand is no stranger to the use of GNSS for grade checking, having used it for surveying for more than 12 years; all told, he’s been surveying for 43 years.
"It’s really user-friendly, really simple and I picked it up right away," he says of the Topcon system. Dandurand says that the grading accuracy of the system is typically within a few hundredths of an inch.
The wetlands remediation is compensating for the impact of construction. You might say that construction of the bioswales will mitigate the impact of increased vehicular traffic.
Don Talend of Write Results, West Dundee, IL, is a publicity and communications project manager specializing in construction, technology and innovation.