Estimation of the Rotational-movement type Landslide Deformation Process based on Comparison between Inclination Rate and Displacement Rate –Inclination

摘要

Landslide deformation process was analyzed by comparing inclination rate and displacement rate in rotational-movement type two landslides. In addition to the Shionokawa Landslide, measuring about 250 m in width, we focused on the Toi Landslide, which is an about 40 m wide colluvial landslide with an inclination rate a digit greater than the former and conducted comparison and analysis of the inclination rate measured with IT ground tiltmeter (PWRI et al. 2009) and the displacement rate measured with extensometers installed on the landslide scarp to make comprehensive evaluation. It then allowed us to arrive at the correlation of y =kx for the inclination rate, x (rad/day), by the backward rotary motion measured with ground tiltmeters installed in the landslide and the displacement rate, y (m/day), obtained from ground extensometers or moving stakes placed at the landslide head. Assuming the correlation is produced by the rotary motion of the radius, r _(2)’ (m), on the ground surface, it then leads to r _(2)’=k =14.6 - 18.0 for the Toi Landslide and r _(2)’=k =35.4 - 42.2 for the Shionokawa Landslide. On the other hand, the rotary motion of the radius, r _(2) (m), estimated based on the estimation from the landslide geometry, r _(2) = about 16 and r _(2)=36 respectively, leading to almost the same results with r _(2)’. For a landslide with rotary motion predominantly observed, it is suggested that the comparison and analysis of the displacement rate and inclination rate contributes to clarification of the deformation mechanism of the landslide. Further improvement in precision of estimation of the deformation process of a landslide that has an arc-shaped slip surface or of the shape of the slip surface is expected by those analyses and the method to estimate slip surfaces obtained from moving stake observation.