Journal of the Japan Society of Erosion Control Engineering, Vol.58,No.4,2005
Occurrence of landslide in the landslide dam bursting processes
Toshio MORI Tatsuhei ITOU Takahisa MIZUYAMA Akira ODA
Abstract
When landslide dams are formed, it is demanded to predict flood discharge accurately.
Therefore it is necessary to judge if landslide occurs inside the landslide dam
during overtopping]erosion processes. The horizontal length of landslide dams
is generally long when compared with the height, and the downstream slope is milder
than the angles of repose, which denotes low possibility of landslide occurrence
inside the landslide dam. Furthermore, when the sediment of landslide dam is coarse,
as erosion by overtopping flow proceeds, the eroded sediment by overtopping is
deposited on downstream slopes and the slope becomes more stable against the outburst.
However when the sediment of landslide dam is fine or cohesive sand, or torrent
gradient is steep enough to generate debris flow, the sediment will not be deposited
on lower reach of the slope. In these cases, the possibility of landslides will
increase according to the erosion proceeds. We investigated how the dimensions
of landslide dams (the length, the height and the gradient of the downstream slopes)
and the soil parameters of landslide dam's material (cohesion, the internal friction
angle) influence the landslide dam's safety factor. Also, the conditions (the
shape of the landslide dam and the soil parameters of the material) of slide occurrence
are considered with calculation of safety factors using different calculation
condition. As a result, we found out that downstream slope gradient and dam height
have the strong influence on the safety factor of landslide occurrence. Moreover,
it is indicated that outburst may occur even with low water level at the upstream
area of the landslide dam when the sediment is fine.
Key words:landslide dams, outburst of landslide dams due to landslides, calculation
of stability based on soil engineering
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