Characteristics of the displacement of a landslide with shallow sliding surface in a heavy snow district of Japan

Abstract

The displacement of a landslide with shallow sliding surface in a heavy snow district was automatically monitored for over 4 years by a newly developed displacement gauge. Meteorological properties, meltwater and/or rainfall (MR), water equivalent of snow and other factors were simultaneously observed. Pore-water pressure was monitored but only for a limited period of time since the displacement of the landslide was too large. Statistical analyses showed that maximum daily displacements of each year were observed not in snow melting periods but immediately before or at the beginning of a snow cover period. There are three types of annual variation pattern with peaks in mid-November to mid-December, mid-April and mid-July. The variation pattern of displacement from the beginning of March to the beginning of June showed the least total displacement of those three types. Therefore, snow cover is likely to affect the displacement of a landslide. Detailed investigation of the landslide displacement during snow cover periods showed that the rate of displacement slowed as the snow cover deepened, meaning a decrease in MR and increase in water equivalent of snow. The displacement ratio for the unit antecedent MR effect during snow cover periods dropped when the snow started to accumulate on the ground in all 4 years. The reduction was likely attributable to snow load since it was found to have a negative logarithmic relation with the water equivalent of snow. Changes in pore-water pressure and the relationship between pore-water pressure and displacement during the snow cover periods differed from those in the other periods. Therefore, the displacement of a landslide that has a shallow sliding surface in a snowy region was considered to be affected by snow accumulation conditions, especially water equivalent of snow.