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ROLE OF GEOTECHNICS IN EARTHQUAKE ENGINEERING

The large earthquakes over the years have left many lessons to be learned whichare essential in putting forward countermeasures or policy to mitigate similarcalamities in future. The degree and nature of damage incurred by earthquakesdepends largely upon states of social developments of the region in which anevent occurs. The topography, ground water conditions and subsurface soilconditions are also important factors influencing features of the damage causedby great earthquakes. Needless to say, the most important would be theintensity of shaking of the ground at the time of the earthquake. There are somany factors as above to be considered that it is practically difficult to forecastthe intensity of shaking and the level of the damage resulting form anearthquake at a given region.

Under the inherent circumstances as above, the earthquake engineering hasbeen developed by reflecting on bitter experiences of calamity that occurredduring past earthquakes. In this sense, the earthquake engineering could becited as experience engineering. It is thus mandatory for engineers to carefullyinvestigate the damage feature, exercise deep insight into causes of the incident,come up with good ideas for mitigation and to implement them in the retrofitworks that follows. The experiences should be reflected as well onimplementation of countermeasures for existing facilities and structures andfurther on in renewing the design codes and regulations in future. It is withoutsaying that the geotechnical engineers specializing earthquake engineeringshould recognize themselves to carry this responsibility and in this sense learninglessons from past earthquakes are the most important things assigned to our

profession.

Since individual earthquake has its own characteristics, it would be necessary tolearn new lessons as large earthquakes occur. In the development of earthquakegeotechnology, for example, Niigata Earthquake in Japan 1964 could be cited asa milestone event in that it has first demonstrated the importance of liquefactionin sand deposits in bringing about various kinds of damage to the ground itselfand structures thereupon. The subsequent earthquake in 1978 in Japan off Izupeninsula triggered the breach of a tailings dam located in the mountaintop,leading to widespread contamination of river beds downhill. The liquefaction ofsand containing silt with low plasticity fines was first identified to be of

importance as well in generating a state of liquefaction in silty sand deposits.The Kobe Earthquake in Japan 1995 would be cited as the first event where man-made islands suffered catastrophic damage along their periphery where quaywalls have grossly moved seaward involving large amount of soil deposits behindthem. The lateral spreading of once liquefied soils was found to exert trulydetrimental effects on the structures and facilities existing on such laterallymoving soil ground. Since then, problems related with lateral spreading havebecome a subject of extensive studies and discussions in the international arenaof the earthquake geotechnics.

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Performance of structures resting upon, or foundations embedded in liquefieddeposit or those undergoing lateral spreading is now one of the major issues ofconsideration for which some solutions and consensus are in urgent need. Thedamage by the earthquakes may be divided into two groups, structural injurydue directly to inertia force during intense shaking and indirect damage due to

liquefaction or lateral spreading of the ground. The features of these two kinds ofdamage have been found different between developing and developed countries.In the developed countries, seismic code or regulations for earthquake-resistantdesign has been put forward mainly for structures and implemented in the designof medium to large-scale buildings or facilities. Thus, the structural damage hasbecome less and less pronounced and implementation of anti-seismic design isrecognized to have contributed greatly for reduction of distress duringearthquakes. In contrast, in developing countries codes or regulations have notyet been put into effect sufficiently and death tolls or property damage resultmostly from the collapse of poorly constructed houses or buildings.

With respect to the geotechnics-associated damage, mitigation measures havenot yet been implemented both in developed and developing countries to anextent to reduce the damage. Consequently, the damage due to geotechnicalorigin such as liquefaction and landslides forms a major part of the distress byearthquakes. From considerations as above, it may be mentioned that theground damage due to liquefaction and landslides is still the cause of majordamage not only in developing countries but also in developed region of theworld, and there is a plenty of challenges emerging from one earthquake afteranother that is worthy of notice and requires further studies before relevantsolutions become of use for mitigating the distress resulting from largeearthquakes. In this context, geotechnical engineers should be encouraged toseek the problem areas and try to come up with some solutions in thisunexplored area.