Framework for susceptibility analysis of layered rock slopes considering the dimensions of the mapping units and geological data resolution at various map scales

In Taiwan, the failure of rock slopes has caused the catastrophic loss of lives and property. To understand the risks associated with rock slope failure, susceptibility analysis has been widely adopted as a fundamental task. However, currently, most susceptibility analyses have investigated only landslide occurrences and have been limited to the regional scale. In this case, susceptibility maps cannot provide detailed information about the rock slope stability as required by the engineers. To fill this gap, this study developed a methodological framework to analyze the susceptibility of layered rock slopes from regional to local scales. In each map scale, the appropriate size of the slope unit (SU) was produced as the mapping unit through the object-based image analysis (OBIA) method, and the susceptibility map was generated with an explicit purpose according to the resolution of geological data. Multiscale susceptibility analysis of layered rock slopes was performed in a metamorphic area in northern Taiwan. The performance of the susceptibility maps was validated by the field investigations and the data of the geologically sensitive area, which were released by the Central Geological Survey of Taiwan. The results show that different phases of the evaluation of rock slope stability were addressed, including the landslide activity and the rock slope characterization on the regional scale and the failure mechanisms on the local scale. In addition, suitable SUs can also be semiautomatically reproduced by the OBIA method with suggested strategies.