Yoshimichi Yamamoto

VERIFICATION OF THE DESTRUCTION MECHANISM OF STRUCTURES IN SRI LANKA AND THAILAND DUE TO THE INDIAN OCEAN TSUNAMI

We surveyed disaster situations in the west coast of Thailand and the south coast of Sri Lanka where damage due to the Indian Ocean tsunami of December 2004 was severe, and investigated the destructive mechanism of structures due to the tsunami. The results we obtained were as follows:(1) If a tsunami with a ground-level inundation depth of more than two meters attacks a lowland extending several hundred meters or more inland, severe disaster will occur. In this case, mortar and brick buildings 30 cm or less in thickness will be destroyed.(2) The stability of a building can be estimated using the easy stress calculating method by assuming a gatetype Rahmen building model and calculating dynamic water pressure.(3) Destruction of revetments and seawalls is caused by incident wave pressure or return flow. In this case, the stability of a coastal structure is mainly determined by the balance of water pressure and earth pressure.

TRIAL OF AN EVALUATION METHOD OF THE BUILDING DAMAGE BY TSUNAMI

In order to develop a rational methodology to evaluate building damage caused by tsunamis, first, disaster data collected in Thailand, Sri Lanka, and Japan are introduced as verification data. Next, the applicability of an empirical method of predicting inundation depth ( = the inundation height from ground level) based on analysis of those data and a numerical simulation method of tsunami flood is examined by comparing calculation values with the verification data. Then, the validity of a convenient method of evaluating building strength against the tsunami using the gate-type Rahmen Building Model is checked by comparing calculation results with actual damage and diagrams to get pillar widths or wall thicknesses at the breaking threshold for common sizes of buildings are proposed.

TRIAL OF DAMAGE EVALUATION BY INDIAN OCEAN TSUNAMI IN PATONG BEACH OF THAILAND

A huge tsunami caused by the giant earthquake occurred off Sumatra in Indonesia, on 26th December 2004, attacked the coastal regions of many countries facing the Indian Ocean. This paper describes evaluation methods of structural damage in order to mitigate the damage by huge tsunamis. First, the damage by this tsunami at Patong Beach in Phuket province of Thailand is explained. Next, diagrams to get critical inundation heights which break buildings are shown by using a rigid frame model as functions of inundation heights. Then, how to get the inundation height empirically is explained. Moreover, a numerical model to simulate the inundation height is also used, because the method described previously will give inundation heights of low accuracy as geographical feature becomes complicated. Furthermore, there were some structural collapses (a masonry wall and so on) by tsunami back-flow; the stability of a concrete wall against the back-flow is also discussed.

Propose of a suction rate formula of backfill from the front lowest edge of a coastal dike by big waves

In the case of coastal dikes and seawalls in a beach or a shallow area, there are a few of field cases that those were destroyed directly by strong wave force and a lot of field cases that scour in front of them and suction from their bodies caused by the continuing action of waves bring their destruction gradually. Therefore, it is important for us to establish the prediction methods of the scouring rate in front of them and the suction rate from their bodies. In this research, we propose a suction rate formula of backfill from lowest edge of a coastal dike by big waves .

DAMAGE LIMITATION OF A COASTAL DIKE AND A SEAWALL

It is important to know the threshold of the cross-section area of a beach to which a coastal dike and a seawall will come to suffer damage. Therefore, the actual conditions on coastal damage are investigated about 33 beaches in Japan and Thailand. Then, the marginal sizes of the beach required in order that those coastal facilities will not suffer damage to each incident wave are clarified. Moreover, since there are many cases that the destructive mechanism of the dike and the seawall on a sand area or a very shallow area cannot be explained by only the stability calculations of these facilities, scour and suction also need to be taken into consideration. Hence, a practical method of predicting the destruction of the dike or the seawall by using the wave overtopping rate to it and the net effective shearing resistance force in its sucking part is proposed. In addition, the availability of a countermeasure which strengthens the net effective shearing resistance force by using small stones as material of the sucking part is confirmed.