Hazardous and tough-to-reach areas create difficulties for geotechnical experts assessing locations along our nation’s roadways. Unmanned aerial systems (UAS) offer a potential solution to these challenges. Many States are evaluating UAS technology to see how it can make project development safer, more cost efficient, and more effective.
The New Hampshire Department of Transportation (NHDOT) funded a research project through the University of Vermont (UVM) that assessed the use of UAS across the Department. The project’s final report includes eight case studies describing potential improvements UAS can make in the condition assessment and stability evaluation of rock slopes along routes in the State and other use cases.
Route 302 in Crawford Notch, NH, contains a 100-foot high rock cut-slope that has a poor overall stability rating. Traditionally, rock structure conditions affecting stability of rock-slopes are mapped using manual measurement. This involves dangerous work using rope access. Introducing UAS to the process allowed engineering geologists to capture rock-structure data in areas only accessible by rope or too difficult and dangerous to reach at all.
UVM collected 310 high-resolution images during their UAS flights in Crawford Notch. NHDOT used photogrammetry techniques, one of its A-GaME methods for rock-slope characterization to create a detailed 3D point cloud model. This technique is faster than traditional methods and the sheer number of measurements obtained by analyzing photogrammetric data provides better characterization of rock structure conditions, resulting in a more comprehensive stability analysis of the cut.
Data analyzed from the 3D point cloud easily transfers into other software for further analysis, visualization, and future access. Using detailed 3D models like these allow engineering geologists and geotechnical experts to make better-informed decisions regarding the stability of new cut-slope designs and geologic hazards from existing rock-slopes.
Measurements taken over time can also help detect changes in rock slopes. Geotechnical asset managers can detail these changes and will have the ability to monitor slopes for movement that may indicate future rockfall releases or rock slides.
The Crawford Notch, NH, case study is available online. To learn more about how your agency can incorporate UAS into its programs, contact James Gray, FHWA Office of Infrastructure. To learn more about photogrammetry and other advanced geotechnical methods in exploration (A-GaME), contact Ben Rivers with the FHWA Resource Center.
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