UAVs for monitoring, investigation, and mitigation design of a rock slope with multiple failure mechanisms-a case study

Slope instabilities adjacent to transportation corridors require timely and precise assessment to determine the risk to road users, particularly when weather changes trigger these instabilities. In southern Alberta, Canada, near the town of Drumheller, a 500-m-long, 60-m-high slope adjacent to Highway 837 has a history of slope instabilities that includes rockfalls, frozen soil falls, and debris flows. The slope failures have blocked the road which increases user and maintenance costs. Due to unsafe conditions and the steepness of the slope (1H:1V inclination), it was only possible to undertake visual assessments of the slope conditions from the road. Advances in unmanned aerial vehicle (UAV) technology have resulted in a quick and safe tool for collecting detailed photographic records of the slope conditions. The combination of UAV data and photogrammetry methods allows engineers to remotely, safely, and quickly perform a precise assessment of the slope instabilities. The paper demonstrates the use of UAV-derived data to evaluate the following: critical instability areas in practice; the magnitude of instability events; the relationship between the drainage network and slope instabilities, and models for rockfall trajectory analyses. The paper also provides a methodology that can be implemented on other slope instabilities to support the decision-making process to define mitigation actions that are practical and minimize associated risks.