Small Flume Experiment on Deep-seated Landslide Collapsed Material Movement

Hefryan S. KHARISMALATRI, Yoshiharu ISHIKAWA, Takashi GOMI and Katsushige SHIRAKI

Previous researches revealed that inflow angle and stream gradient are two major factors that distinguish the formation of landslide dam and debris flow from collapsed material of deep-seated landslide. Yet their significance mobilization of landslide material has yet to be clarified. This research aimed to clarify the influence of inflow angle and stream gradient on rapid deep-seated landslide collapsed material movement and the possibility of landslide dam formation by using small flume apparatus. The small flume consisted of inflow segment and main channel where the junction angle between them were modified into 0°, 30°, 60°, and 90°, while the gradient of the inflow segment and main channel was fixed on 45° and 10° respectively. Experiment was conducted on 6 classes of water content, namely from 0% to 100% with 20% increment. Soil samples from Nigoridani, Nara Prefecture where deep-seated landslide occurred in 2011 due to Typhoon Talas, with D50 of 7 mm and saturated water content of 21% was used in the experiment. The result revealed that on its saturated water content, collapsed material formed deposition at junction area of 11%, 14%, 32%, and 49% on inflow angle of 0°, 30°, 60°, and 90° respectively. The deposition on inflow angle of 60° and 90° was relatively significant and possibly forming landslide dam. In contrast, the material was mainly transported to the lowest part of the flume as debris flow on inflow angle of 0° and 30°. The experiment result confirmed that collapsed material of DSL that encountered large inflow angle will experience large collision with the opposite slope which cost a large amount of energy and thus the material deposited at or near the junction area. Water content also has an important role in determining the mobilization of landslide material.

2018/1 132-138