Shallow slope failure is one of the common sediment disasters in Taiwan. The size and range of a shallow slope failure depend on topographic and geological conditions, such as soil depth and bedrock topography
(soil-bedrock interface). Thus, the methods for detecting the soil–bedrock interface need to be established before predicting
or estimating the size and range of shallow slope failure occurrence. In this study, we selected three sites on
colluvial slopes. First, we verified the applicability of electrical resistivity tomography (ERT), cone penetration testing
(CPT), and geological boring methods for detecting the soil–bedrock interface at a site with a shallow slope failure.
Then, we applied ERT and CPT to investigate the bedrock topography at two large-scale sites. Based on the information of the boring cores, we confirmed that CPT can effectively detect soil depth and the soil–bedrock interface.Moreover, the characteristic of electrical resistivity that changes greatly between soil and bedrock layers can be used to detect the soil–bedrock interface. For large-scale investigations, it is sometimes difficult to estimate the location of the soil-bedrock interface because electrical resistivity varies greatly in the colluvial layers and electrical resistivity is sensitive to electrode arrays and the complexity of the colluvial environment. Because CPT is economical and convenient for a large-scale slope environment, we therefore suggest that the combination of ERT and CPT is an effective way to detect the soil–bedrock interface in a colluvial environment.
Key Words : Cone Penetration Test, Electrical Resistivity Tomography, Geological Boring, Soil-bedrock Interface.