BIM and Civil 3D - Fact or Fiction?
When Christopher Fugitt asked me to write an article for AUGIWorld on AutoCAD® Civil 3D®, it was with utmost enthusiasm that I accepted this gracious offer. Over the years I’ve been asked time and time again – “What is the difference between Civil 3D and BIM?” This question is evidence that the infrastructure and land development industry has struggled with a Civil 3D/BIM identity complex. An Autodesk executive recently reflected to me, “…that train has already left the station.” It is my intent with this article to shed some much needed light on AutoCAD Civil 3D and its relationship to BIM.
BIM for the Infrastructure Professional
There have been countless articles published relating to BIM for architects and building professionals. This is not going to be another one of those articles. Sourcing Wikipedia, “Building Information Modeling is a process involving the generation and management of digital representations of physical and functional characteristics of a facility. The resulting building information models become shared knowledge resources to support decision making about a facility from earliest conceptual stages, through design and construction, through its operational life and eventual demolition.”
In other words, when you create a life-size scale building model using Autodesk® Revit, for example, practitioners sharing that model with others can easily design their components to eliminate potential conflicts. This is currently the most common application of BIM concepts, and the industry still has a long way to go. In many instances, opportunities still exist for quantity takeoffs, tender documentation, construction records, and ongoing facility lifecycle management.
These BIM concepts are reasonably straightforward as they apply to buildings. They also apply to the infrastructure and land development industry, but in a different way. Infrastructure practitioners, when describing BIM, sometimes prefer to change the “B” in BIM from a noun to a verb, which implies that we are “building” information modeling into our processes. Fair enough—it is important that we improve our data management practices, but this is still not truly capturing the essence of BIM. This is the root of the problem—the term BIM does no justice to the land development and infrastructure industries, and hence the widespread confusion!
The term Model-Based Design is one that is used quite often when applying BIM principles to the fields of infrastructure and land development engineering. Regardless of what you call it, the terms are applicable to infrastructure within the following contexts:
- Leveraging data throughout infrastructure procurement phases
- Leveraging data within an individual project phase
- The Local Government asset data repository
The concepts of BIM, as they are applied to engineering project lifecycle, data leveraging within a specific phase, and the government asset data repository, are discussed in the following sections.
Infrastructure Procurement Process
As with buildings, infrastructure components—sanitary, storm, water main and roads—have a lifecycle. At the municipal level, the procurement part of lifecycle usually begins with capital planning and ends with capture of “as-built” data and the transfer of this data to the municipal asset register, which in most instances is the geodatabase in their GIS.
A typical infrastructure procurement for a municipal project is illustrated in the following figure.
Figure 1: Infrastructure procurement process
The municipal infrastructure procurement process begins by analyzing data residing in an asset register or GIS to identify and choose the projects to be completed as part of the annual capital planning process. From there, individual projects typically move through the preliminary design, topographic survey, detailed design, construction, as-built data collection, and as-built data reduction (record drawing submission) phases. AutoCAD Civil 3D can be used in all of these infrastructure project procurement phases.
The planning phase is where designers have the greatest ability to affect the outcome, and hence the total cost of the project. Civil 3D is an excellent planning tool as it allows designers to quickly generate and evaluate alternatives to the undertaking. During the topographic survey phase, surveyors can use Civil 3D to automatically reduce data collected in the field to pre-engineering base plans and existing ground surface models.
The next step is detailed design, where design and construction plans are prepared, quantities are calculated, and construction staking data is generated. Detailed design and construction drawings are then sourced for construction staking data—where the design is moved to the field. The final steps are the collection of as-constructed data, the reduction of that data, and the submission of that data to update the municipal asset register. All steps can be accomplished using functionality available in AutoCAD Civil 3D.
When you consider BIM, one of the key components is the efficient movement of data throughout the project phases—in this case, the phases associated with infrastructure procurement. As indicated, Civil 3D can be applied to these “process adjacent” phases for infrastructure and land development projects. It only makes sense that data can be re-used (rather than re-created) during these process adjacent phases. For example, data generated during the project planning phase (sewer alignments, road features, and so on) can be reused and modified during the detailed design phase. Model data generated in detailed design can be used for both construction data extraction and the preparation of digital submissions required for updating local government asset registers. This data continuity is the key essence of BIM, as it relates to the infrastructure procurement process.
Individual Project Phase
The individual project phase for infrastructure and land development projects is another candidate for the application of BIM principles, as data sharing can be done from a centralized model. As with buildings, infrastructure projects consist of many different components—sanitary, storm, water, roads, and electrical—all of which are designed in a modeling environment.
This modeling environment, in which data is shared and not duplicated, allows for the following:
- Natural propagation of design changes through dependent drawings and documents
- Cross-discipline collaboration to eliminate design conflicts
Just as the building designer needs to ensure the plumbing doesn’t conflict with the electrical and HVAC, infrastructure designers must ensure utilities are designed based on depth requirements so they don’t conflict with one another. Once again, this utility and road conflict resolution represents a key component of BIM being applied to infrastructure and land development projects.
The critical BIM component within an individual project phase is data sharing versus data duplication. The methods of data sharing that AutoCAD Civil 3D supports are summarized in the following bullets:
- AutoCAD External References – graphical data sharing
- Civil 3D Data Shortcuts and Reference Objects – sharing surface, alignment, profile, pipe network, and view frame data
- External References, Data Shortcuts, and Reference Objects – for creating cross sections in separate drawings
- External References – labeling Civil 3D data “through” and external reference
- Survey Database – sharing survey observation, point, and figure data
- Autodesk Vault – multifaceted data management and sharing for drawings, project objects, and project-related files
Your project may involve some or all of the above data sharing techniques. The key is to define those relationships prior to beginning a project so that all involved can clearly understand the data structures and standardized mechanisms for data sharing. The mechanism used for data sharing is referred to as the drawing/ data architecture, or the structure of the data.
An example of the drawing/data architecture for a simple project using AutoCAD External References, AutoCAD Civil 3D Data Shortcuts, and Reference Objects, is shown in Figure 2.
Figure 2: Data sharing in Civil 3D
For projects with multi-disciplinary and multi-designer input, it is imperative that data is shared versus duplicated. This data sharing element is yet another important aspect of BIM that must be considered for infrastructure and land development projects.
Infrastructure Lifecycle Management
As stated earlier, lifecycle management is yet another key component of the BIM concept. Where lifecycle management for infrastructure and land development projects differs from building/architecture is that the data is not stored in the CAD model, but in the asset register, which for many local governments is the GIS. It is in lifecycle management that the parallels between buildings and infrastructure begin to break down.
It is at the end of the infrastructure procurement process where the data representing the “as constructed” conditions are input into the asset register. The emerging problems within local governments is that these asset registers often take on several meanings—CAD, GIS, infrastructure maintenance management systems, financial systems—with the same data residing in multiple registers. Once the as-built data is in the asset register, then the process for continuing infrastructure lifecycle management can begin—basically making the decision as to whether is cheaper to replace or renew.
As can be seen, the concepts of BIM, which were initially founded in the building industry, can readily be applied to infrastructure and land development projects. The key lies in understanding the processes and applying those concepts to the individual components of the process. Whether it’s BIM or Model-Based Design, the concepts are the same and the technology allows designers to share and leverage data in certain areas. With Civil 3D the true BIM components lie in: 1) moving data through the various phases of the infrastructure project procurement process; and 2) sharing data during individual project phases.