SHEAR STRENGTH PROPERTIES OF SAMPLED SOIL OF THE YABAKEI LANDSLIDE, JAPAN

The Yabakei landslide occured in the pyroclastic deposit area, Oita Prefecture, Japan on April 11, 2018. Landslide are well known to occur frequently during heavy rains and snowmelts, but the Ybakei landslides occurred when there was no rainfall.The soil samples taken from scarp were examined by the physical test and the ring shear test.

In the results of the physical test, The soil density is 2.382g/㎥,and Particle size distribution is clay fraction (<2 μm), silt fraction (2-20 μm) , fine fraction, coarse fraction (200-2000 μm), and gravel fraction (> 2000 μm)of the soil sample were 16.8%,24.1%,31.7%,10.7%,16.7%

In the relationships between the friction coefficient and the displacement D, gradually decreased with the shear displacements, and in = 100 kPa, the residual friction coefficient is = 0.351,at D = 195 mm and in = 250kPa, it reached to = 0.229 at about D = 220 mm.

The parameters of fully softened strength (φsf ) and residual strength (φr ) were estimated to be 32.5° and 19.3°, respectively .

Stability analysis was performed utilizing these shear strengths and occurrence mechanism of the slide was discussed.