Advancing with Machine Control
November 27, 2006
The right civil engineering application can be a powerful tool when tackling the surveying and design requirements of a complicated infrastructure project. But increasingly, civil engineering applications can be used to add value in another way: prepping machine control data. At my firm, Cole & Associates of St. Louis, Mo., we have taken our civil engineering applications to the next level. We provide clients with a full range of civil engineering and land development services, and have learned to use our civil software not just for design work, but for machine data prep. Recently, we successfully completed a road project in St. Charles County, Mo., that highlighted our implementation of this software.
County RoadwaysLocated just 30 miles west of St. Louis, St. Charles County has experienced tremendous growth over the past few decades. In 1970, less than 100,000 people lived in St. Charles County. Today, census estimates place the local population above 320,000 with more than 7,000 new residents moving to the area each year in the last decade.
This rapid growth has necessitated extensive improvements to the regional infrastructure, particularly the roadways. Some of these roads are managed by the Missouri Department of Transportation (MoDot), while others fall under the jurisdiction of Transportation Development Districts (TDDs) created by municipalities to keep up with the population growth. Cole & Associates has worked with local municipalities, MoDot and the TDDs to help create these roadways by providing a variety of surveying, design and data prep services.
Design BenefitsThe roads in yellow (pictured on page 32) are part of the Dardenne Prairie, Mo. TDD led by Opus Northwest LLC of Minneapolis, Minn., a full-service real estate developer serving the northwestern region of the United States. Cole & Associates designed the roads in this project using Autodesk (San Rafael, Calif.) Civil 3D modeling software, which serves civil engineering design, drafting and GIS needs for transportation, site, sewer, storm drain and subdivision projects. On several of the road segments, we developed machine control models for the general contractor. For several years, my colleagues and I have been using innovative applications such as Autodesk Land Desktop, Autodesk Survey and especially Autodesk Civil 3D for our civil engineering design needs to accelerate the pace of projects while delivering the highest quality service to our clients.
One of the primary advantages of Civil 3D is that all of the design elements are linked dynamically. For example, on the Dardenne Prairie project, when we needed to change a ditch elevation, we were able to do so in 10 minutes versus the two hours that would have been required had we used older tools. Additionally, Cole & Associates was able to take advantage of the customizable features of Civil 3D to add functionality to quickly label cross sections. By customizing upfront, we were able to effortlessly take information out of CAD files, plot it into our cross sections and add relevant labels and information. The time saved, once again, was significant: a process that could have taken two days took less than four hours.
Data Prep ProcessDuring our data prep work for the MoDot project, we also experienced other benefits of using advanced software. The impact of our use of Civil 3D went beyond the design phase. Civil 3D helped support the use of machine-controlled equipment in the construction phase, an increasingly common method of working on the jobsite.
Because Civil 3D data is largely based on dynamically linked 3D models, changes required for models to be used effectively in the field can happen much faster. Being able to load the data more quickly into the earthmoving equipment is a huge time and cost benefit for both contractors and clients. The application also helps Cole & Associates stand apart from its competition.
As the first step of the road project, we created an alignment, the horizontal location of the roadway. We also created the profile that depicts the vertical location, and then the typical sections along the roadway. We then created additional calculations and data to accommodate super elevation parameters and/or warpings for non-typical elements.
In Land Desktop, we developed routines to interact with Microsoft Excel to calculate very complex super parameters or elevation changes for features, such as ditches, that were pushed back into Land after being calculated in Excel. We were able to refine the process using in-house developments in Land and Excel. With custom macros, we extracted and pushed Profile Grade Line (PGL) elevation data from Land Desktop's civil design module into Excel to calculate sampling section locations. We then used a combination of calculations and additional routines/functions to push in various data for widths of a zone or slopes of pavement for each zone, ultimately generating both profile and sometimes alignment offset data for each zone. Land Desktop reads these Excel-generated data for profiles and for horizontal alignments as needed with one "swing of the bat" for each alignment.
Alignments, profiles, typical sections and design constraints combined together were then fed into Land Desktop to create a 3D model, which was further refined into a digital terrain model (DTM) surface, adding complex grading scenarios and tie-ins. Once we had a model and surface, we exported them to a machine capable file, which can be imported directly through software for specific machines.
Many companies are producing hardware and software for the machine control arena. Luckily, the machine control vendors write third-party functions for both Land Desktop and Civil 3D that allow the user to export to the appropriate format that data must be sent to. Each vendor uses a slightly different format.
The general contractor we worked for on the MoDot project, Fred Weber Inc. (Maryland Heights, Mo.), uses Trimble (Sunnyvale, Calif.) SiteVision on its dozers and Trimble BladePro on its graders, so we exported our data in Trimble's format.
Using Trimble Link software, the 3D road section model was exported to a Trimble-specific cross section file format containing horizontal alignment, vertical profile and typical section (template) data. We then exported the surface DTM to a Trimble surface file called a TTM. We also produced a background linework file depicting proposed improvement features such as edges of pavement, curbs, sidewalks, pipes, structures, etc.
Programs like Trimble's SiteVision allow the operator to see the background file on screen while driving down the alignment. When cutting or filling, he can see the blade location versus where the machine data is programmed to cut or fill. On machines that are equipped to drive the blade, the operator can put the controls in automatic mode when they are close to grade and they will control the blade based on the 3D model data. We have always built our models to the finished ground without considering the depths of materials, which can vary across roadways depending on the road's type and function. By building to the top surface for all roads, the contractor has the flexibilty to change pavement depths in the field on the equipment's software to accommodate the various depths.
General contractors have been quick to embrace machine control once they see how it can help them complete projects faster and within budget. I have also seen them hire their own GPS and machine control experts to do most of the data assembly and upload/maintenance for their equipment after a firm produces the 3D models for them (e.g., DC, TTM and background DXF linework files).
We began to really appreciate the benefits of Civil 3D and its dynamic 3D models on the TDD roadway project. Since the data made for generating cross sections resides in a model-based environment called a corridor, adding data to make machine ready files was much simpler than with our old tools. Civil 3D's flexible super elevation parameters and open customizable sub assemblies allowed us to really fine-tune our model building techniques. We no longer needed to use Excel to calculate complex roadway sections. As a roadway design tool, Civil 3D worked more efficiently than Land Desktop.
Forging Ahead with Machine Control So what are the time- and cost-saving benefits of using applications like Civil 3D for data prep? For one, it is an excellent way to check our data ahead of time--before digging starts--to avoid costly mistakes. During the MoDot project, we found an issue with the alignment while we were entering data into the model. We took corrective action and solved the problem right away. By doing a thorough check ahead of time, Cole & Associates ensured that once the general contractors started working, the construction process would continue until completion. As a result, the project avoided undue delays and remained on schedule.
Many vendors are only beginning to embrace the idea of using their civil engineering applications for machine data prep, but the practice is growing in popularity. From making sure that data has been prepared correctly, to speeding up the design process, the right civil engineering application plays a key role in increasing the effectiveness of our firm and enhancing the level of service we provide to our customers.