In the landslide regions of the green-tuff areas in the Tohoku District, clay samples relating to slip planes (sliding surface) were collected, and investigation and observations were carried out the viewpoints of soil engineering and mineralogy.
As a result, montmorillonite was identified in clay mineral samples from most of the regions, while, the quantitative values were not so high as initially estimated. Further, it was suggested that characteristic trend in montmorillonite due to regional difference, phase and component rocks may depend upon the composition of montmorillonite (smectite).
The data of each clay mineral sample was found above and in parallel to A line in the plasticity chart in most case, and the specimens from mudstone tended to be higher in liquid limit and plastic limit compared with the speciments from tuff. These results reveal high probability that the clay samples relating to these slip planes may have been formed by burial diagenesis, and later, by weathering in land area.