A Model Corridor
July 1, 2010
A slight sense of déjà vu came over project managers as they entered the field for the Interstate 94 (I-94) North-South Freeway Project in Wisconsin last June. They hadn’t physically walked the project area before. However, they had been able to visualize the field in advance through 3D models of the site.
“These terrain models are ‘machine- control’ accurate, meaning they are 100- percent accurate horizontally and vertically to the proposed design geometry and, in fact, are an exact 3D replica of the entire construction area and plan from start to finish,” says Daniel Kucza, PLS, a survey manager with Milwaukee-based Kapur & Associates. “Building a digital model of the project before starting construction allows managers to preplan operations such as mobilizing field crews, coordinating materials and traffic logistics, and devising construction schedules as well as giving them the opportunity to identify and rectify any plan discrepancies to avoid build mistakes in the field. So when they get onsite, they already have a feel for it and can immediately start to work.”
That foresight, combined with advanced survey technology, has been particularly beneficial for the teams on this project. For if ever there was an infrastructure project perfectly aligned with the definition of “stimulus,” the I-94 project would be it.
It’s been nothing short of “stimulating” for the myriad crews pushing to meet the $60-million reconstruction project’s aggressive timelines--deadlines that were advanced specifically because it was awarded federal stimulus money--against the backdrop of one of the state’s main arterial roadways. “Originally, this project was designed as three separate projects that were to begin in 2011, but the stimulus package led the Wisconsin Department of Transportation (WisDOT) to combine the three projects into one and push the start date to mid-2009, which nearly halved our typical construction time for some portions of the project,” explains Tom Collins, project engineer with Collins Engineers Inc. (CEI), the Milwaukee-based engineering firm representing WisDOT for the I-94 project.
“The models helped us develop efficient timelines because we could preplan--we already knew where we could retrieve and store materials and how we were going to minimize trucking and traffic--so we could avoid downtime during construction. And the Trimble GPS and total station survey technology have enabled us to lay things out more quickly and construct more quickly with less errors so we can make sure every hour of every day has counted.”
Indeed, crews have not only been able to meet the project’s tight deadlines, they have also been a testament to the value of basing a project on a real-world model--from preplanning, to scheduling, to constructing, to quality control, to real-time communication--and enforcing the benefit of 3D with smart surveying techniques in the field. Based on its overall success, the I-94 project may become the construction-management model for future infrastructure projects.
Three for the Price of OneThough I-94 stretches 385 miles across the state of Wisconsin, the I-94 project focuses on a 35-mile section of the roadway that lies in the southeast and connects Milwaukee in the North to Kenosha in the South. First constructed in the late 1950s and early 1960s, this interstate has outlived its paved life. With about 1.3 million people, 28,500 businesses and 595,000 jobs located in this area, the growing amount of rubber rolling along the pavement--more than 217,000 vehicles a day--has led this critical road network to become congested and hazardous to motorists. WisDOT recognized that the corridor’s design and pavement deficiencies could no longer be strengthened by resurfacing campaigns; with projected traffic volume increases of 30 percent by 2035, it was clear that the interstate required a full redesign and reconstruction.
Initially, the 35-mile mainline project was divided into numerous separate projects that were scheduled to begin in 2011 and be completed by 2016. But then the American Recovery and Reinvestment Act (ARRA) was initiated, and suddenly WisDOT had the opportunity to acquire federal monies to financially secure the I-94 project and expedite its schedule.
That meant, however, that WisDOT needed to restructure some of the independently planned and designed projects into “shovel-ready” projects, presenting team leaders with a unique challenge. “Taking separate plans and combining them into one 1,400-page plan set makes it difficult for us to accurately interpret building instructions and have a consistent and comprehensive view of the whole project,” says Jason Wong, a project manager with Walsh Group, the lead construction contractor for the first I-94 project stage. “Compounding the challenge was the fact that the project was let late in the year, so we only had six months to complete the first year of construction.”
Indeed, the first project stage to hit the road was a 4.5-mile section of I-94 running north of the Wisconsin/Illinois border, a low-lying area characterized by wetlands and protected wildlife species along with a fair share of drainage issues.
Knowing the team would need a very precise blueprint for planning and executing the project, Walsh turned to Kapur to transform the integrated plan sets into one cohesive “shovel-accurate” model for earthworks, design and construction.
Modeling a PlanKapur used Trimble Terramodel visualization software to create two 3D models of the finished grade and subgrade; the latter was produced to accommodate slope differences from the subgrade to the finished grade because of drainage concerns. Although the models are typically created from existing plan sets, this project involved the integration of multiple projects, so Walsh wanted to have an extra layer of quality control to validate the existing terrain data and subsequent volume quantities calculated from that data. As Kapur began creating the models, a survey team used Trimble R8 GNSS rovers and Trimble S6 total stations to cross-section the entire project corridor to check the accuracy of the existing survey data and, if necessary, to correct any errors.
Kucza says investing the time to model the project first helped WisDOT and Walsh to save time and money in the field. “Transforming the 2D CAD data and existing topographic data into 3D allows us to readily identify any data discrepancies or inconsistencies--those potential ‘gotchas’ that can cause construction mistakes--and resolve them before anyone puts a blade in the ground,” Kucza says. “That removes any assumptions or misinterpretations in the field regarding the accuracy and quality of the survey data, allowing them to construct more quickly from day one with more confidence.
“It also enables them to quickly and accurately calculate the volumes of earth material they will need to remove and import as well as the resources required to meet those numbers,” he adds. “That helps them control their costs--they don’t want to have to move dirt twice.”
Sensitive to the wetlands in the project area, the data-rich models enabled Walsh and WisDOT to prepare environmentally sound strategies to mitigate risks to wildlife and to control water runoff as well as develop cost-effective strategies for streamlining the significant earthworks operations. “One challenge of this project was that we had to recycle all of the old pavement and bring in 400,000 cubic yards of fill from other surrounding areas to build our embankments,” Collins says. “With so much wetland in this corridor, we were confined as to where we could store materials. The models allowed us to think ahead and look at our sequence of operations to determine where we could stockpile materials on the job and how to place them in a way that would not affect other parts of construction.”
With the aggressive timelines inherent in the contract, Wong says the model information also helped them to devise effective work plans and schedules in advance.
A New Level of VerticalWith attack plans in place, it was time to set ground control.
Focusing first on the horizontal ground control, a two-person crew pounded in rebar every 500 to 1,000 feet along the project’s 4.5-mile corridor and set GPS coordinates on each rebar point using Trimble R8 GNSS rovers and WisDOT’s WISCORS RTK network. The network of 35 permanent Trimble NetR5 GNSS reference stations and Trimble VRS technology provided RTK GPS data in real time to within a 2-centimeter accuracy. “With the availability of the WISCORS VRS system, we were able to pick the local datum inside the Trimble TSC2 collector, navigate directly to a control point and be within five hundredths of a foot from day one,” Kucza says. “That’s very rare.”
Kapur’s team then set up a Trimble DiNi Digital Level to acquire height measurements of each rebar point to obtain an “extremely tight” site calibration. “Highly accurate vertical control is very important when you’re using GPS machine control because GPS has inherent error,” Kucza says. “Using a digital level, we ran an eight-mile circuit and achieved a miss closure of only two-hundredths of a foot−almost negligible over an eight-mile circuit. That allowed us to establish an extremely accurate vertical calibration for our control network and for our grade and ground profiles.”
Both 3D grade models were then set to the site-control calibration and uploaded to crews’ TSC2 data controllers and grade control systems in Walsh’s earthwork equipment. The models gave field teams a front-row seat to visualize the end product at the outset of the project, making it easier to map out high-priority areas, delegate equipment and assign crews before their Caterpillar excavators and bulldozers dug dirt.
With the common data models held in the TSC2 controllers, project managers also had the anchor tools to adopt Trimble’s Connected Site approach in the field--a technology model designed to seamlessly manage diverse data streams from different tools to help users reduce rework, increase productivity, utilize assets more efficiently and improve planning cycles. According to Kucza, unifying all field teams through data and communication devices allows crews to work autonomously and efficiently and leads to far better coordination, speed and production in the field. “Because we had qualified models and calibrations uploaded into every TSC2 controller, we could hand anyone a GPS rover, and as they navigated across the project it would tell them where they were and where the proposed roadway needed to be,” he says. “That’s a real comfort, and it’s a far more efficient way to work.”
The Pathway to PavementIn parallel with preparing the bottom stone layers of the interstate, the Kapur team had to stake out points for concrete paving, barrier wall paving, curbs and gutters, storm sewer hubs, and other features. Surveyors used the Trimble S6 robotic total station to ensure they’d achieve the vertical accuracy required. “The S6 provides a very high degree of vertical accuracy, which we needed on this project,” Kucza says. “Our concrete stakes needed to be within two hundredths of a foot vertically. With the benchmarks set from digital leveling, the S6 laid out more than 28 lane miles worth of concrete pavement, and every stake was within a quarter-inch vertically.”
The thickness of the roadway was also important. “Contractors not only want to make certain they have sufficient material to ensure the expected life of the roadway, they also want to know exactly how much concrete they’ll need because it’s quite expensive,” Kucza explains. “So every hundredth that we’re off in concrete layout is a percentage of the yield. When you are putting in $20-million worth of concrete, one or two percent of error is a lot of money.”
Using the Connected Site approach, field data were continually integrated into the portable TSC2 data controllers as all of the pockets of activity rolled along. In this way, the “back office” was constantly connected to the front lines, which helped managers build and maintain a well-orchestrated assembly line of mini projects, monitor work in real time and adapt to needed changes.
With the core 3D construction blueprint keeping everyone on the right path and the advanced survey technology keeping crews on course, field teams successfully completed the first phase of the I-94 project on time. The new four-lane southbound corridor was opened to traffic last December.
Construction on the northbound section began in March and is scheduled to be completed by the end of 2010. That second phase is also being anchored and guided by 3D models and Trimble survey technology to again help WisDOT create and maintain an integrated and efficient workflow while minimizing downtime and reducing rework.
“It used to be that we’d go into the field without a prebuilt model or a detailed plan for construction,” Collins says. “Here, we have created a whole system that lets us study the topography, validate information and identify any issues prior to construction. Then during construction, we have the data references and survey technology to quickly perform quality control and monitor progress. And we have the connected communication to help us better inform the public of the project’s status.”
Wong agrees, noting that the models and technology allow the team to plan ahead and schedule work more efficiently instead of spending time on the jobsite looking for the information needed to do the work. “Once construction begins, we can resolve issues more effectively because we have the 3D terrain layout and elevations to run if/then scenarios to ensure a fix isn’t going to adversely effect some other part of construction,” he says. “It empowers us to react quickly and confidently.”
A slight sense of déjà vu at the start probably doesn’t hurt, either.