Influence of Buttressing and Lateral Confinement on a Large Block Prior to Rockfall

ABSTRACT: Rockfalls are a source of danger for infrastructure near rock slopes containing potentially unstable blocks. Rockfalls can cause property damage, road blockages, and harm to people. Literature studies that monitor rock slopes have helped to demonstrate connections between rockfalls and the precursors that indicate potential instability. After identifying these precursors in potentially unstable blocks, measures can be taken to stabilize or remove the blocks to mitigate the risk to infrastructure near the slope. This study aims to evaluate the influences of buttressing effects and lateral confinement from nearby rocks on block stability through numerical modeling of a 76 m3 rockfall. Prior to the rockfall, a series of smaller rocks near the large block were displaced in association with loosening of the large block. To create the model, the topography of the block and surrounding area was digitized using photogrammetry. The rockfall process itself was simulated using the distinct element method, such that the rockmass is modeled as an assemblage of distinct blocks with boundary interactions between each block to account for the discontinuous nature of the rockmass. We used the model to evaluate trends in displacements of the block of interest with and without the presence of the surrounding smaller rocks. 1. INTRODUCTION Rockfalls are a common hazard in mountainous areas, particularly along roadways adjacent to steep rock cuts (Copons and Vilaplana, 2008, Abellan et. al., 2010). Efforts have been put into place to monitor dangerous rock slopes, including by using LiDAR and photogrammetry to track slope change over time (Abellan et. al., 2013; Kromer et. al., 2015; Lim et al., 2005). Photogrammetry has been used as a tool to detect rockfall activity in both natural slopes (Graber and Santi, 2023) and cut slopes (Walton et. al., 2023). One possible end-use of such monitoring data is for forecasting of future rock falls that can be mitigated before they occur. However, forecasting of rockfall events is only possible if rockfall precursors are understood (Kromer et. al., 2018, Royan et. al., 2015). One potential precursor is the occurrence of small rockfalls before a larger failure. Monitoring of precursory rockfalls has been studied as a potential method of spatial and temporal prediction of rockfalls (Rosser et. al., 2007, Royan et. al., 2015).