Geoscience Reference
In-Depth Information
Fig. 5.27. Superstructure before and after test
4.3.2. Representative test results
The superstructure became inclined after the final test (Figure 5.27). The piles yielded
andbucklednotonlyattheirheadsbutalsoatdepthsfrom0.7mto1.2mduringthefinal
stage of shaking resulting in permanent deformation and inclination of the superstruc-
ture. The direction of pile deformation corresponds to those of the strong axes of ground
displacementandacceleration,indicatingthatthegrounddisplacementaswellasinertial
force had a significant effect on the failureof piles.
5. Earthquake loading aboard geotechnical centrifuges
Laboratory testing of small scale models is a particularly fruitful avenue in earthquake
geotechnical engineering due to the paucity of data collected during real earthquake
events which are both rare and often unpredictable. However, the particularly strong
dependency ofstrengthandstiffnessofsoilontheconfiningstressdictatesthatthemod-
elsneedtobetestedunderrealisticstressesandstrains.Thiscouldbereadilyachievedin
a geotechnical centrifuge, provided suitable shaking tables that can impart strong earth-
quakeloadingtothemodelsin-flight,canbemountedontothecentrifuge.Thistechnique
is generally termed as dynamic centrifuge modelling and has been widely used in USA,
Europe, and Japan.
About 30 large geotechnical centrifuges (radius larger than 3m) are in operation in the
worldcarryingoutmanyakindoftestsonfooting,piles,tunnels,retainingwalls,slopes.
The payload capacityofmanyofthecentrifuges isbetween 1and 2tonsand models can
be testedbetween 100 and 200 gravities.
Centrifuge model testing of the effect of earthquakes on geotechnical structures and of
liquefaction of soils has been pursued actively worldwide. Of particular interest to many
researchers are soil liquefaction and lateral spreading and their effects on a variety of
geotechnical structures. Of the 32 geotechnical centrifuges listed in Japan by Kimura
(2000),severalofwhichwereinstalledaftertheKobeearthquake,15wereequippedwith
shakers. The percentage of research papers devoted to earthquake modelling in the Cen-
trifuge international conferences also attests to the increasing importance of this rather
new field(Figure 5.28).
