On March 14, 2022, a landslide occurred in Yanaizu Town, Fukushima Prefecture, Japan. This landslide is notable in that it occurred during the snowmelt season in the distribution area of Tertiary tuff, so-called “Green tuff”. Field survey and measurements were carried out for this landslide. In this paper, it is described those results and the examination of the process based on them. The results are as follows ;
The excavation works were carried out on this slope until July 2021 and the slope was stabilized. This slope was composed of tuffaceous coarse-grained sandstone, “Green tuff”. A tuffaceous siltstone beds were distributed in this sandstone layer with a dip structure. This layer deteriorated due to slaking with stress relaxation associated with construction work. In addition, topography and groundwater infiltration conditions had changed. The rise up the groundwater level during the snowmelt season acted on this situation, triggering the slide. These processes are confirmed by slope stability calculations.
”Green tuff”, which is widely distributed mainly in eastern Japan, is known to contain smectite clay minerals such as chlorite. The “Green tuff” layer looks rocky, and its slopes seem mechanically stable. However, it is necessary to pay attention to its deterioration, when the tuffaceous siltstone beds are distributed into the slope.
