Study on destruction type of training dike by large‐sized sandbags stacking used after debris flow disaster

Hiromi AKITA, Nagazumi TAKEZAWA, Fumiaki AKAZAWA, Hiroshi NISHII, Yasuo ISHII and Ryo HIRATA


The training dike of large‐sized sandbags stacking are often used for emergency remedial works in the steep mountainous area following debris flow disasters. According to the existing reference standard for the construction of temporary coffering design, it is applied under the condition that the flow velocity is under 2.0m/s and only water flows down. However, those sandbags in the steep mountainous area are exposed both to water and sediment loads with flow velocity generally exceeding 2.0m/s. To evaluate the stability of those sandbag‐based structures under different flow conditions, we firstly employed a flume experiment to examine the destruction types of the structure, by changing channel gradient and angle of dike for flow. The movement of those sandbags exposed to sediment‐laden flow from the upper flume was monitored with installed cameras and laser sensor. Secondly, we conducted safety factor calculations based on experimental results and limit equilibrium method. As a result of the flume experiment, the movement of the stacked sandbags are categorized into two patterns: outflow of individual sandbags at the lower end and the slide of all staked sandbag. From the result of the safety factor calculation, it could not be evaluated that the safety factor in the limit equilibrium state is 1.00. However, when the safety factor decrease, sandbags stacking slide and the lower end sandbags outflow. Our findings suggest that the stability of those structures should be carefully considered when applied for emergency remedial works in steep channels.

Key words

large‐sized sandbags stacking, emergency remedial works, debris flow, flume experiment, limit equilibrium method