Methodologies for Effective Slope Failure Reconnaissance

This paper presents best practices for conducting a slope failure reconnaissance investigation. Over the past 3 years, thousands of landslides and mudflows have occurred in the Southern California region, which have been primarily related to heavy rainfall (including locations where slopes have been denuded by wildfires). These slope failures have resulted in major damage to structures, roads, and utilities. Proper repairs to the damaged slopes and infrastructure can only be completed after the cause and nature of the slope failure are investigated (e.g., failure geometry, extent of failure, potential propagation of failure, and earth materials). An effective investigation requires the collection of a significant amount of information in a time-sensitive manner. There are various methods of non-destructive data collection, including remote sensing (e.g., LiDAR, photogrammetry, and thermal imaging), visual inspection for indicators that may signify a contributing cause of the failure (e.g., exposed scarp face, wetted areas, and condition of utilities), and interviews with witnesses, residents, and/or property managers. There are also multiple methods of subsurface intrusive testing available to evaluate the conditions, extent, and strength of the slide mass and intact material. In order to monitor the presence and rate of potential movement within and outside of the hypothesized landslide area, various types of instrumentation devices can be installed. This paper provides a detailed description of these methodologies that can be used to perform an effective slope failure reconnaissance investigation.