2023 年 16 巻 2 号 p. 22-35
The strength of a slip surface is an important parameter when considering countermeasures against landslides. However, the shear strength of slip surfaces is difficult to determine directly owing to the small number of samples of the slip surfaces themselves. Therefore, the back-calculating method has set shear strength parameters without a clear basis. In this study, the shear strength obtained from natural and pseudo-slip surfaces was compared with shear and physical properties to clarify the validity of the shear strength of pseudo-slip surfaces (artificially cut and shaped specimens made from the same rock type as the slip surface, boring cores). The experimental methods used included mechanical tests such as cyclic direct shear test, and direct box shear, as well as surface observation of the sheared surfaces using a scanning electron microscope and measurement of surface roughness using three-dimensional surface analysis. In the sandstone, the shear strength (based on one-sided shear tests) for grit size #150 (abrasive grain size of sandpaper 125 μm) obtained a clear correspondence with the fully softened strength of the natural slip surface, and for grit size #600 (abrasive grain size of sandpaper 28 μm) with the residual strength of the natural slip surface. Therefore, in the future, the shear strength of pseudo-slip surfaces is expected to replace natural slip surfaces because of the simplicity of testing and the fact that it reflects the properties of the rock types.
