Abstract
We have measured the pore water pressure in the sliding face and the velocity of displacement of the sliding layers at Hirayama landslide area. The findings of the investigation on the measurement data, are as follows;
(1) When the static pressure due to ground water in the slide face has over 0.8kg/cm2 by the heavey rains, the slide of layers begins.
(2) Accordingly, the dynamic pore water pressure occurs in the sliding face: this value uw is shown in the following formula.
uw≥0.65Pe
in the formula mentioned above, Pe is effective overburden pressure, but uw disappears within a short time.
(3) About the same time uw disappears, the internal friction angle of the crush rocks in the fall zone decreases with permeation of rainfalls and the amount of passive earth pressure due to crush rocks increases rapidly, which continues to put pressure on the layers. Accordingly, the velocity of displacement of the layers can be expressed by the Bingham's formation.
After several days, sliding layers have stopped by a progression of drainage from the drainage tunnels.
