Owners, including departments of transportation, often define the parameters for common features as conditional instructions in standard specifications, captured in spreadsheets. The specifications for a Type I retaining wall, for example, may contain consistent dimensions for the footings, specific requirements for the footing toe, and adjustable dimensions for the height of the footing wall.
VDC software uses packets of commands called subassemblies to read the spreadsheets, along with the 3D topographical file or laser scan, and parametrically model features, road surfaces, retaining walls, typical road details, bridges, grading standards, rail tracks, utilities, trenching methods and more, based on real world information—not guesses or assumptions.
By using a VDC model, estimators can calculate every foot of trench from exact existing elevations and exact trench depths and apply a slope formula to figure out the exact amount of excavation required. The set of commands in the trench subassembly can incorporate intelligent commands like, “start at the invert elevation of the pipe at the current station,” and the next command can be “if the existing grade is more than twenty feet, build trench A. If it is less than twenty feet, build trench B.”
Fourth and Fifth Dimensions
Modeling projects properly during the estimating process also allows construction teams to send VDC models to subcontractors to facilitate the development of shop drawings and allows the incorporation of subsidiary models and schedules—the fourth dimension (4D); and budget—the fifth dimension (5D)—to the three dimensional model and to begin construction immediately after receipt of the notice to proceed.
Other Advantages of VDC
1. Project managers and superintendents may use quantity information generated by VDC models to create work plans and generate daily reports.
2. The public can view models to visualize and monitor construction activities and coordinate travel and work plans.