Prepared for Takeoff
August 2, 2010
Known locally as “The Big Build,” Sacramento County Airport’s Central Terminal B project is easily the largest capital improvement project now underway in Sacramento. Expected to be completed in 2012, the $1.3-billion project includes a new central terminal (and the demolishing of “Terminal B,” considered antiquated), a new automated people mover (APM), new parking lots and access roads, and dozens of significant, albeit less showy, improvements to runways, taxiways, a 21-gate concourse and support areas.
Andregg Geomatics, a surveying and mapping firm based in Auburn, Calif., has been working on the site since 2006, beginning with control, topographic and design surveys, and continuing with staking and as-built surveys. The firm has also provided perimeter control points for machine-controlled grading. In that time, the project crews have learned a lot about airfield security protocols, taxiway safety procedures and other peculiarities of airport work. They’ve also developed new techniques and workflows that help crews work efficiently in a highly controlled environment.
“We started working on the airport project just for the county, doing design and control surveys,” says Andregg Project Manager Michael Farrauto. “Our work has now expanded to include the three main contractors and all the staking they need. There have been a variety of challenges, like vertical control issues in an area that subsides, photogrammetry control, topographic and design surveys on the ‘airside’ of the field, and very precise staking for some parts of the project, such as the people mover now being built.”
To do the work efficiently and be responsive to four large clients, Andregg has depended heavily on a tightly integrated Trimble Connected Site solution using interlinked hardware, software and services primarily from Trimble. Equipment used includes several generations of Trimble GPS receivers, Trimble S6 robotic total stations, and the Trimble VX Spatial Station, which was used for some scanning and as-builts. Trimble Access Field Software and the Trimble Connected Community Web Service were used to link field surveyors to the office crew that performed point processing with Trimble Business Center Software. “The link between field and office was important,” Farrauto says, “because security procedures made it time-consuming to enter and exit the airfield. With the cellular link to the office, I could get a request for new point calculations, and the points could be downloaded right into the party chief’s controller without even breaking down his instrument setup.”
By keeping quality high, using an integrated survey solution, adjusting field and office procedures to accommodate lengthy airport security procedures, and using one-person survey crews for the majority of staking work, Andregg has stayed competitive and profitable over a long project lifecycle. By working hard and looking for innovations on one big job, the team has found ways to improve all the work they do.
A Matter of ControlGiven the size of the project and the relative importance of precise elevations in airport work, Farrauto was surprised by the state of the airport’s control network. “There were just a few available high-order bench marks,” he says, “and subsidence is a factor in the whole region. We suggested starting from scratch to get the project on NAVD88, and the airport agreed.”
After conferring with airport officials and contractors to determine the optimum bench mark layout, the Andregg team designed a field procedure that involved simultaneous observations of three federal base network control stations in Woodland, Rocklin and Davis, Calif., and several stations in the proposed airport network. Using four Trimble 4000SSi dual-frequency GPS Receivers, Andregg crews performed 20- to 90-minute fast-static observations over three days, with each station occupied at least twice. All post processing was done using Trimble GPSurvey Software.
A two-person crew then performed level loops with a Trimble DiNi Digital Level, running through the ten bench marks set for the airport network, two available NGS published bench marks, and three Sacramento County benchmarks. A total of 23 miles of backward and forward loops were run over three weeks, with balanced backsights and foresights and daily closing of loops. After more processing and least squares adjustments, Andregg achieved an average vertical precision for all lines to all stations of less than 0.991 ppm, an average horizontal error of 0.0037 meters, and an average vertical error of 0.0023 meters for leveled stations.
In the end, the airport and Andregg had reliable, accessible vertical control that improved the efficiency and accuracy of all subsequent work; the vertical control could also be used to extend additional high-precision control. To ensure that all this work would last as long as possible in the airport’s mucky, subsidence-prone soils, special care was taken with the bench mark monumentation. Six-inch diameter PVC wells were set with aluminum covers, and 9/16-inch stainless steel rods were driven to refusal--in one case, 52 feet of rod was used. The visible bench marks are 3-inch brass caps custom made by Berntsen International. Andregg took one more step to preserve the airport’s investment in high-order control: a multi-page record of survey, with coordinate values and station descriptions, was filed in the Sacramento County Recorder’s Office.
Working With Security and Staying OrganizedAlthough the control survey, aerial survey and main design surveys required security clearances, relatively little access to secure areas was needed during these phases. But as crews began to fulfill on-call as-built and design surveys at the request of architects, they also began to spend long periods in the secure “airside” of the airport. This brought a fresh set of challenges.
“It can be difficult to get around on this project,” says Andregg Project Manager Tom Holmberg, LS, who has been the onsite manager for much of the project. “Everyone who works on this project has been fingerprinted, and has had to have background checks and extensive orientation to get their SITA badges. Once you have your badge, you have to wear it everywhere on site and report anyone you see not wearing one.”
Even with the badge, getting around in secure areas is cumbersome. Part of the required orientation for field crews was instruction on when, where and how to work in particular parts of the airfield; there are also numerous gates, checkpoints and restrictions to contend with. All trucks used must have company logos and flashing lights. There are also less obvious factors to keep in mind--for example, survey flagging is prohibited because it might get sucked into jet engines.
What it all means is that Andregg has made a substantial investment in training and equipping the employees that can work onsite at the airport. Their actual working time must be used efficiently to make the most of that investment. “That’s where Trimble Access and Connected Community have been really useful to us,” Holmberg says.
Both products work together to tightly coordinate field and office staff. Access uses cellular modems in Trimble controllers to transmit and receive survey data efficiently; the Trimble Connected Community provides tools to manage data from multiple sites securely and to eliminate redundancy and confusion. Field crews can keep working and send data to the office without returning to a field office or breaking down a setup. Office staff can monitor results and upload newly calculated points as needed, right to individual controllers. This keeps trained, oriented and badged field staff doing the work they’re best at and prevents unnecessary trips offsite with all the required security overhead. It also lets the back office check completed work immediately and provide newly calculated points to crews as soon as they’re available. “It’s made a big difference in our workflow and saved us a lot of time,” Holmberg says.
“When you work on a project like this,” he adds, “with many thousands of points gathered and staked out over several years, it can easily get disorganized. So it’s important to have an organized structure.” Data management procedures are consequently very strict. All notes, calculations and other submittals are independently checked or reviewed. “One person does the work, another person checks the work--we like our procedures to have redundant checks,” Holmberg explains. All notes are scanned, stored as PDF files, indexed by date and easily accessible.
Staking reports, customized in Trimble Business Center, are generated automatically. “Our field crews don’t have to think too much about the reports because they’re largely automated,” Holmberg says. “That helps to reduce errors.” Some work is brought into CAD for review, and as-builts are routinely compared to plan as the as-built is being recorded. Departures from design are instantly flagged. Trimble Business Center and other tools are used to synchronize points automatically, and Holmberg performs additional checks and reviews as needed. To date, there have been no errors due to data confusion.
Photogrammetric and Design SurveyingSacramento is a large airport handling more than 150 flights daily from two main runways that are 8,600-feet long. And since the surrounding area needed to be checked for obstructions, the aerial survey footprint was huge--8,000 feet by 18,000 feet. About 50 panels were set, and the panel layout was planned to minimize entry into secure areas. Since every passage into secure areas required a half hour or more to pass through checkpoints, thinking ahead to minimize entries saved substantial time. The deliverables from the aerial survey were a topographic map with 1-foot contours and digital color orthophotography with 0.25-foot pixel resolution.
Design surveys for the terminal expansion were relatively straightforward except that tolerances were tight: +/-0.05 feet horizontally and +/-0.02 feet vertically. In addition to the feature-rich terminal and support areas, Andregg crews also did topographic surveys of more than 1 million square feet of taxiways, aprons and runways.
Right-Sized Crews“Robotic instruments, and integrated surveying in general, are a big part of the reason we’ve been able to stay profitable on this project,” Farrauto says. Crew sizes have varied depending on the work being done. When setting panels for the photogrammetric work, two- or three-person crews were typical, and six crew members were needed for the simultaneous GPS observations required during the control survey. About 80 percent of the topographic surveying and construction staking has been done by one-person crews. “For most of the civil work we do, one-person crews are fine and are the most efficient way to go,” Holmberg says. “But for things like anchor bolts and gridlines, where we’re basically splitting hairs and using target cards and peanut prisms, I like to assign two-person crews because I feel we get better results.” Holmberg also says that some employees simply like working by themselves and that this is the best way to let them work.
Just as crew sizes are adapted depending on the work, technology is freely switched depending on the task at hand. But Farrauto does believe in using equipment and software from one firm. “We used to have a few different brands around, but since we integrated on one source we’ve seen real economic gains,” he says. “On this job, the GPS receivers, the S6 and VX stations, and even the digital level we used for control loops all came from the same source--and that was a big help. Assigning one controller to each party chief for all our equipment is very efficient and makes the most of our crew’s training and their ability to work alone. And a consistent software system that automates data management from all equipment prevents a lot of errors.”
Meeting the Challenges“It’s quite challenging to manage this kind of large-scale project with seven or eight contracts running at once and a lot of pressure,” Holmberg says. Farrauto agrees. “These are challenging times,” he says. “To stay competitive and keep winning contracts, we’ve had to be extremely efficient.”
For Andregg Geomatics, staying competitive has meant strict quality control procedures, a Connected Site solution that ties together equipment and software, and aggressive use of technology that dramatically expands the capacity of one-person survey crews. Taken together, these principles have kept Andregg Geomatics working in a difficult business environment.
Editor's note: Numerous firms have been involved with The Big Build project. The landside terminal is being built by a joint venture of Austin Commercial and Walsh, and the airside concourse B is being built by Turner Construction. Additional project partners can be found on The Big Build Project Partners Web site.