An ongoing Oregon Department of Transportation project along Interstate-5, located south of Roseburg at Roberts Mountain, is intended to add additional climbing lanes by widening the freeway. Widening near the summit required reconfiguration of an approximately 90m long buttress at the base of an older landslide. Geology within the project site is entirely within the Dothan Formation, which is a mélange of relatively weak blocks in a highly sheared matrix. Realignment of the buttress called for short sections to be removed and replaced into the new buttress configuration. After beginning construction, traditional slope monitoring indicated increasing movement. At this point, the lead geotechnical engineer worked with IDS GeoRadar and SkyGeo to implement a risk management program that included monitoring of the site using ground and satellite-based radar.

On October 4, 2019, shortly after ground radar installation, movement above the first buttress slot-cut began to accelerate. Over a five-day period with work on the buttress continuing, peak surface ground movement velocities, as measured by the radar system, increased from 29 to as much as 68 mm/day. Seeing that the movement was accelerating, ODOT’s Construction Office worked with the Project Contractor to halt work and quickly backfill the slot excavation. Radar velocities were corroborated with in-ground Micro-Electro-Mechanical-Systems (MEMS) arrays located within exploratory borings which penetrated the landslide mass. This initial movement encompassed a mass in the toe area approximately 74m wide by 45m tall. Over subsequent months, active movement progressed up to the original headscarp and widened the lateral limits by an additional 15m. The radar system captured additional movement as a series of smaller blocks shifting downslope to rest against the initial mass. The individual radar images have been combined to produce a video that provides an animated illustration of how this coalescing landslide behaved. A second example of successful early warning of large landslide movement occurred on June 26, 2020. In the early morning, the radar measured deformation on the slope which correlated to an area of active buttress removal. This area approached speeds of 15 mm/hour and shortly after detection, cracks appeared on the slope and operations were put on hold for further geotechnical investigation by ODOT.

Wide area satellite radar images from the ESA Sentinel-1 C-band system monitor for project-wide displacements on natural and project influenced slopes. This unique opportunity to capture active events is being used to leverage our use and knowledge of ground and satellite-based radar monitoring.