IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS002 Poster presentation 1795
Mechanism of damage to road embankment caused by tsunamis
Mr. Hiroyuki Fujii
Dep. Coastal eng. INA corporation, Japan
Nobuo Shuto
The Golden 24 is a universal law to save many human lives when a catastrophic disaster occurs.
Damage caused by such a huge tsunami as the 2004 Indian Ocean tsunami is a good example. It is
quite important to send rescue teams, medical assistance and vital goods as many and as soon as
possible to the damaged areas. In order to support such human activities in an emergency, a hardware,
i.e., coastal roads, is a vitally necessary infrastructure. Among several causes of coastal traffic
hindrance, the present paper aims to understand the physical mechanism of damage to road
embankments made of soil in order to find how to reinforce or improve them. There are two major
causes of damage to soil embankment. The one is scouring due to overflowing tsunami. The other is
erosion near bridge abutment due to tsunamis that concentrate to openings. A rough estimate whether
a road embankment made of soil would be damaged or not was given by one of the present authors as
a function of the height of embankment and the overflow depth. In order to explain more in details, a
numerical scheme to simulate the process of scouring is developed, on comparing with large-scale
hydraulic experiments for river dikes for which the overflowing time is much longer compared to
tsunamis. The hydraulic experiments carried out in the Public Works Research Institute, Ministry of
Construction, revealed; (1) the critical depth appeared near the shoulder, then (2) the flow separated
and reattached. (3) After the reattachment, the flow over the rear slope was supercritical. (4) When the
flow hit the toe of embankment, high impact pressure was measured, and (5) a hydraulic jump
appeared to return a sub-critical flow. This process is simulated in the numerical model by the present
authors, except for the flow separation and reattachment near the shoulder. Calculated shear stress, if
compared with the strength of the embankment soils, shows the area that should be covered by solid
materials. When a tsunami is stopped by a road embankment of long extension, the flow concentrates
toward openings such as rivers, canals and channels. The velocity of the concentrating flow is simulated
to compute the shear stress on the embankment slope. The slope near the bridge abutments should be
covered by such structure as wing walls to resist the tsunami-induced shear stress. This simulated result
may give a measure of the length of the wing walls. The model proposed herein paper also provides a
basis to examine the usable road network that is the fundamental factor of emergency response
Keywords: coastal road, soil embankment, wing wall