Photogrammetric 3-D Rock Slope Modeling, Discontinuity Mapping, and Analysis Utilizing an Unmanned Aerial Vehicle

Abstract

Description

An Unmanned Aerial Vehicle (UAV) was utilized to collect aerial photography of a hazardous cut rock slope located on the north shore of the Monongahela River in Glassport, PA. The road cut under investigation is over 100 feet tall and 2,700 feet long. This exercise is directed toward gaining an understanding of the local geology (bedding, lithology, fractures, and joints), including the structure and stresses within the rock. Three-dimensional photogrammetric slope modeling and discontinuity mapping were utilized to help identify and organize rockfall hazards.

Applications

The commercial intent of this exercise was to conduct a rockfall hazard analysis for the Pennsylvania Department of Transportation. Further iterations of this modeling may be used to project geologic structural data down into the subsurface. Surface outcrops have long been used as analogs for the subsurface, allowing petroleum geologists to understand depositional systems. The ability to bring this information into the office in a true three-dimensional model, integrating it with seismic data or wells logs, is a powerful tool. While the end product of our workflow is an engineering/ geologic hazard analysis, the path to get there produces information that is useful to petroleum geologists as well.

Results and Conclusions

Through our analysis, we have identified distinct lithological units that experience different modes of failure; resistant Morgantown Sandstone undergoing planar failure and weaker Clarksburg Claystone undergoing wedge failure. A hybrid failure is possible in the lithologic units between the above-mentioned layers.

Technical Contributions

Though methodologies and case studies exist for similar work-flows, we have optimized our work flow to improve upon existing procedures. The flight plan was designed to maximize exposure to the rock face and fracture and joint orientations as discerned in a previous field visit. Traditionally, this type of work has been conducted in large rock quarries using stereo-pair imagery and ground based cameras at a large distance. The utilization of UAV’s allows for resolution of one-half inch or less and ensures data is collected without distortion from the base of the slope to the top of the outcrop. By utilizing our work flows over a large expanse, perhaps coupled with multispectral imagery to distinguish lithologic boundaries and mineralogy, the process described may be utilized for large scale structural mapping and analysis.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018