The ABCs of AMG
by Michael Ross PLS/PSM
April 29, 2011
3D models provide a 360-degree perspective on the design.
In the past few years, a new world of construction has emerged, created in part by the challenging economic times of the recession. To remain competitive in this new world, more contractors are using technologies, such as Automated Machine Guidance (AMG), to help lower the cost of construction and increase productivity on the project site.
In case you don’t know, AMG enables construction equipment to be controlled automatically by an on-board computer to achieve design grade. Positional information, which is obtained from either a satellite-based GPS or a ground-based laser, is acquired by a receiver on the grader and transmitted to an on-board computer that precisely controls the position of the cutting blade. In addition to the on-board computer, various sensors and meters determine precise positioning of the cutting blade (for cross-slope correction and rotation angle), and grade corrections are applied to the cutting blade multiple times per second. Accuracies of 0.10 foot can be realized with GPS and 0.02 foot with laser-based technology.
Data Behind the Technology
Design issues are discovered during the modeling process, not during construction.
Models need to be sufficiently densified for today's machine-control applications and properly georeferenced to the project site. Surveyors have historically prepared design data for field layout and can readily interpolate between the 2D paper world and the 3D world of construction. Having a surveyor prepare the 3D model also provides another layer of quality control between design and construction.
Creating a 3D model begins with the receipt of the original design plans from the engineer. Design components, such as alignments, profiles and typical sections, are recreated in a 3D environment that allows the technician to view the proposed design from all perspectives. These design components are georeferenced to the project site to ensure their correct placement in the field.
As the model begins to take shape, quality checks are performed on it to ensure compliancy with the original design. Issues discovered during the modeling process are documented and reviewed with the design engineer. All revisions from the original design are documented, dated and stored with the project to maintain a record of the model. This process enables design issues to be corrected before mobilizing equipment to the project site, which is one way the contractor can save on costs.
Preparing the Data
Site materials can be managed more efficiently with a 3D model.
In order to create this complex roadway model, a series of design templates was generated to accommodate the variable roadway widths, transitions and areas of superelevation within the design corridor. Utilizing the templates, surface models were generated for all phases of roadway construction (rough grade, subgrade and final grade). The new 3D design data was then merged with a surface model of the existing site to create a final 3D model suitable for construction and volumetric analysis.
Reports and cross-sections based on the new design model were generated that ensured full compliance with the original design specifications. The deliverables for this project included a Digital Terrain Model (DTM) formatted for the contractor’s AMG equipment, a CADD file containing 3D polylines of the design corridor and a point file for layout of proposed features not suitable for AMG.
AMG also eliminates survey stakes as obstacles on the project site.
Using GPS rovers, the contractor can quickly and easily check a grade or lay out a feature for construction without a surveyor. AMG has also enabled the contractor to move materials faster with less-experienced equipment operators. With the increasing cost of materials and labor, combined with the ever-decreasing project budget, the benefits of AMG cannot be ignored. In this new world of construction, it's only a matter of time before this technology becomes commonplace on the jobsite.
Michael Ross PLS/PSM
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