Abstract
When we calculate the safety factor of landslide, we usually uses the ground-water level as pore water pressure. Since there are many landslides in Japan and the field observation needs a very long period, it is almost impossible economically for the landslide engineer himself to measure the pore pressure by piezometer in every landslides. Conveniently, we use the ground-water level as the pore pressure in stead of measuring it directly.
The author observed the variation of ground-water level precisely at Chausuyama landslide area from 1971 to 1973, and found that seepage force cannot be neglected in the case of using the ground-water level in stead of pore pressure. If we rely upon only the ground-water level as the indicator of the variation of the safety factor, it is very dangerous.
