UAS-Enhanced Rock Mass Characterization of the Left Abutment at Madison Dam, Ennis Montana

Recently, advancements in drone technology for mapping rock mass features have been on the rise and are becoming more of a staple for geotechnical site investigation. The safety of humans when collecting field data is a top priority and using drones, or unmanned aerial systems (UAS), can minimize those safety risks. Creating models that depict accurate data of rock mass discontinuities and possible failure modes in inaccessible areas has its challenges, but drones can provide a way of addressing those challenges. This study involves using UAS-based data collection to capture rock mass fractures at Madison Dam just North of Ennis, Montana. A manual flight capturing video data and three autonomous flights capturing photos were performed on-site on December 7, 2023. In the autonomous flights, the camera was pointed primarily vertically downward. During the manual flight, the camera was directed toward the steeply inclined rock face, in a more horizontal orientation. Both methods of data collection provided data for a complete point cloud model using a photogrammetry software package called Pix4DMapper. In addition to the modeling, a series of rock characterization and analysis was performed using samples from the field and joint set data collected from the drone imagery. Testing included a multistage triaxial test to determine the shear strength of the intact rock, as well as a series of kinematic analyses generating possible failure modes of the rock mass. The results from this study indicate that the rock at Madison Dam is highly fractured and has a possibility of failure. Introducing drone photogrammetry can be time efficient and pose much safer human conditions for creating real-time data from the field. Although there are challenges when collecting drone imagery data, it can give helpful data to the engineering community when needing data from places that are dangerous for human access.