Stability of Volcanic Slopes in Cold Regions

Rainfall- and earthquake-induced failures of slopes formed by volcanic soils occur frequently in Hokkaido, Japan. This study aims at clarifying failure mechanisms of volcanic slopes caused by both rainfall and freeze-thaw action in cold regions such as Hokkaido. Additionally, the mechanical behavior of volcanic slopes pre-deformed due to cyclic loadings such as seismic loadings were examined to elucidate the effect of initial water content on rainfall-induced failure of volcanic slopes. Using model slopes of different shapes constructed with volcanic soils, a series of model tests was conducted under several conditions in which spray nozzles and a shaking table were used to simulate rainfall intensity and cyclic loadings. Test results showed that surface failure of volcanic slopes differed depending strongly on their initial moisture content. Based on the results of model testing, the effects of freezing and thawing and cyclic loadings on mechanisms of rainfall-induced failure were drawn upon to propose an evaluation method for slope stability. The model test results indicated that rainfall-induced failure can be uniquely assessed by changes in water content in zones subjected to freezing and thawing or to shearing deformation due to cyclic loadings.