Figure 1: Point clouds from 3D laser scans are combined with design elements in a virtual model of Portland, Ore.'s Sellwood Bridge.national Airport. ational Airport.
Sundt Construction Inc. is at the forefront of using building information modeling (BIM) solutions and applying virtual design and construction (VDC) to vertical construction projects such as office buildings. Now they are transferring lessons learned on those projects to horizontal infrastructure projects, transforming their approach for the construction of highways and bridges. Sundt is working to design the best construction solutions for project owners by facilitating communications, reducing change orders and requests for information, eliminating rework, increasing productivity and quality, shortening schedules, generating more intelligent as-built data, and – most importantly – reducing costs.
VDC is a process aimed at enhancing collaboration between participants at all levels by using intelligent models that provide insight for creating and managing infrastructure projects. Sundt first recognized the benefits of using VDC, which better enables conflict identification, while working on light rail projects. Similar to clash detection on HVAC and other systems in vertical building projects, VDC allowed Sundt to model and detect conflicts between underground utilities such as sewers and water lines. Performing clash detection on transportation projects is extremely critical because (unlike vertical projects that are usually unoccupied until completed) builders of most transportation projects need to minimize safety risks and unplanned delays since projects must accommodate traffic during construction.
The benefits of using VDC on these initial projects encouraged
Sundt to expand the use of model-based processes for all horizontal construction projects and investigate construction technologies and methods to improve capability, efficiency, and quality. After a year of research, development, and testing, Sundt now relies on model-based workflows to help complete its transportation projects and uses AutoCAD Civil 3D, Autodesk Revit software products, and Autodesk Navisworks Manage software to support VDC.
Sundt has found advantages in creating construction-ready models during pre-construction of infrastructure projects and believes that the models have the potential to transform all phases of the construction process – from surveying to paving to recording as-built information and everything in between.
Vertical building construction processes often are repeated and repeatable. For example, builders may use the exact same formwork when placing concrete decks on two separate buildings. The same trusses and supports used to support one deck can be used on the floor above as well as on a deck at a project across town. However, the inherent complexity of horizontal projects prevents the creation and use of single static elements of a model over the entire scope of a project. The design and construction of highways, bridges, roads, and associated utilities are more complex because of the unique surface conditions on every project and the need to tie into existing infrastructure elements. A single section of a road can easily have more than 10 different conditions that can change in a short span.
Therefore, the use of a virtual project model – a model that intelligently responds when existing conditions and/or design elements change – is arguably more important on horizontal transportation projects than on vertical building projects and provides numerous benefits throughout project construction.
Capturing existing conditions
On a recent heavy civil project, Sundt used 3D laser scanning to obtain existing conditions information. Obtaining a 3D laser scan of the project site creates millions of very precise measurements that together create a point cloud accurate to within a millimeter that represents real structures and objects. These points can be imported into software such as AutoCAD Civil 3D, enabling users to navigate through a 3D model of the points and take measurements. This process allows estimators to combine the laser scan of existing conditions with a preliminary design model, helping them explore and evaluate proposed construction methods such as project phasing, traffic control, excavation sequencing, and material selection. Instead of spending time calculating quantities by hand, estimators can focus their efforts on adding value by delivering the best solutions to project owners.
For example, Figure 1 (page 53) shows the existing conditions of a bridge reconstruction project in Portland, Ore. Since the models were created within a 3D virtual environment, estimators could evaluate different construction methods without incurring the costs of mockups or prototypes. Estimates created in this fashion can require more time and effort at the beginning, but the resulting models are more accurate and flexible enough to handle many project variables and alternative scenarios.
Building intelligent models
VDC modeling environments, such as Civil 3D, feature parametric subassemblies and corridor modeling. Subassemblies are small, intelligent sets of instructions that electronically depict road surfaces, retaining walls, typical road details, bridges, grading standards, rail tracks, utilities, trenching methods, and more. Subassemblies are stored in libraries and inserted into the model as needed. Corridor modeling combines horizontal and vertical geometry with these customizable, cross-sectional subassembly components to create parametric 3D models. These subassembly components parametrically change in appropriate ways to accommodate the specific application.
For instance, estimators can change a shored trench to a single bench trench at the click of the mouse in an effort to explore quantity, productivity, and cost impacts. Beyond selecting general shapes such as vertical or stepped sides, Civil 3D users also can specify parameters such as slopes and distances. Laser scanning improves the process further since it provides up-to-date information on the existing terrain instead of relying on outdated data.
On an army hospital project that involved preparing the site work, including the roadways, Sundt estimators needed to evaluate different scenarios for placing sewer pipe 45 feet below grade. Traditionally on this type of project, estimators would have used an Excel spreadsheet that includes information about depth and the existing grade, with the concomitant potential for errors. In contrast, a VDC model allowed the estimator to evaluate the process quickly and efficiently.
Using VDC, the estimator determined that a two-step process, where a scraper digs a large channel wide enough to hold the dirt excavated from a second narrow trench required for the installation of the pipe, would help reduce construction costs. This method avoids the costs and delays associated with placing the dirt in trucks, hauling it to another location during construction, and then hauling it back to fill the trench. With the use of AutoCAD Civil 3D subassemblies, Sundt was able to model an intelligent trench that helped communicate the estimator's idea and quickly generated more accurate quantities. In addition, the same model created during the estimate was accurate enough to help generate survey points, calculate quantities, and drive field activities via automated machine guidance (see section below).
Avoiding clashes and coordinating construction
One of the greatest benefits of VDC is that it facilitates the discovery of clashes and coordination issues within the virtual environment – not in the field – and consequently reduces requests for information and change orders along with the associated health and safety risks. As the project evolves, a VDC model can incorporate fabrication models from subcontractors, helping project teams identify and resolve coordination issues before construction begins and costs are incurred.
For example, on a three-mile-long light rail project through the heart of Phoenix, being able to "see" underground was critical in helping to check that all costs were captured and accounted for in the estimate.
Planning construction phases
Modeling projects properly during the estimating process allows construction teams to link the schedule – the fourth dimension or 4D – and budget – the fifth dimension or 5D – to the 3D model in order to begin construction immediately after receipt of the notice to proceed. A detailed phasing plan for complex steel arches on a terminal expansion at Denver International Airport is shown in Figure 2. Using VDC, a virtual model for this project could be developed that included the physical pieces for installation as well as the order and the phasing of the scaffolding.
|Figure 2: Virtual design and construction allowed development of a detailed phasing plan for complex steel arches on a terminal expansion at Denver International Airport.|
VDC improves collaboration by enhancing communications between participants, allowing them to visualize challenges in an intuitive environment that can be manipulated to illustrate problems and create solutions. For example, when a designer specifies a road width or structural thickness, it is communicated to every stakeholder, and the designer's intent is not hidden in hundreds of pages of project plans and specifications.
VDC also facilitates the creation of animations that more clearly demonstrate construction processes and helps identify the most efficient means of construction. Multnomah County, Ore.'s Sellwood Bridge project, near Portland (Figure 1), is a prime example of this. On this project, Sundt needed a construction plan that would put something in place as soon as possible. The solution that Sundt proposed was to slide the existing bridge more than 40 feet north from its current location, and then construct the new bridge ‘in place'(www.sellwoodbridge.org). This will allow traffic to continue to use the existing bridge while construction of the new bridge takes place, minimizing traffic delays.
Controlling construction equipment
Another advantage of VDC is that once the model is verified and controls are set on the jobsite, operators can upload files containing project alignments and 3D surfaces to computers in heavy equipment such as graders or excavators. The surface model provides operators with information needed to grade roads or dig trenches. A computer screen in the grader or excavator displays exactly where to cut or fill based on the location of the blade or bucket. When work has progressed to the point of the final pass, operators can turn on automated machine guidance and allow computers to make the millions of micro adjustments needed to achieve a perfect grade.
On a recent project that involved lowering the profile of an existing 5,000-foot stretch of Interstate 17 in Arizona, Sundt used the intelligence of the Civil 3D model to guide machine control grading equipment. Traditionally, surveyors needed to manually calculate the points needed to define the road location. On this project, the surface model provided operators with the information needed to grade the roads and dig trenches, automating the process. This process saved time by eliminating the need for survey crews to spend weeks "blue topping" the road (placing wooden stakes to define the top of the grade) and significantly increased the productivity rate of Sundt's equipment and crews because of the constant and direct communication via automated machine guidance.
As part of its commitment to deliver quality horizontal projects to owners on time and within budget, Sundt has demonstrated that VDC improves the construction process and frees skilled professionals to concentrate on creating solutions instead of calculating quantities or fixing problems in the field. VDC enables all participants in a horizontal construction project – owners, architects, engineers, general contractors, subcontractors, suppliers, and the public – to visualize the entire process in a seamless, holistic way and to create innovative techniques to meet increasingly constrained budgets and deadlines.
Eric Cylwik is the modeling engineer for Sundt Construction Inc., Heavy Civil Division. Kevin Dwyer is the senior claims coordinator for Sundt Construction Inc.