Geoscience Reference
In-Depth Information
30
25
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5
0
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2010
Year
Fig. 5.28. Evolution of thenumber of papers presented at the Centrifuge
conferences inthe fields of earthquake simulation
5.1. DYNAMIC CENTRIFUGE MODELLING
Intheearly1990s,significantprogressinearthquakecentrifugemodellinghasbeenmade
within the framework of the North American programme “VELACS” (VErification of
Liquefaction Analysis using Centrifuge Studies). Eight laboratories were associated to
perform several series of very well-designed cross tests on soil liquefaction as well as
to compare the data with numerical model predictions (Arulanandan et al., 1994). Based
on this landmark series of tests, it became evident that repeatability of centrifuge tests
on liquefaction is guaranteed only when the shakers are able to reproduce the repeatable
earthquakeloading.Preparationofthesoilsample(includingsaturation)andofthemodel
alsoexertsastrongeffectonthequalityoftheexperimentalapproach(Madabhushietal.,
2006). In Europe, only Cambridge University (UK), CEA-CESTA (France), and LCPC
up to now have carried out dynamic centrifuge experiments, and with entirely original
systems at Cambridge University and CEA-CESTA.
5.2. SHAKINGFACILITIES AT CAMBRIDGE UNIVERSITY
Recently, the “Stored Angular Momentum” (SAM) actuator (Madabhushi et al., 1998;
Coelho et al., 2006) is being employed. In the SAM actuator, high levels of energy
arestoredinaflywheelspinningatahighangularvelocity.Thankstoafastactingclutch,
the stored energy is transferred to shake the model (Figure 5.29). The SAM actuator
gives the user control of duration, frequency of the tone burst, and intensity of the earth-
quake loading. This system has proved quite successful and has to date produced about
10 PhDs and a significant number of publications. In general, mechanical shaking sys-
temsareinexpensivetobuildandcangeneratestrongearthquakes.Theirlimitsconsistof
the difficulty of mimicking a realistic earthquake input motion during testing and of the
mechanical noise produced. Cambridge University is now starting the development of a
2-D servo-hydraulic shaker to provide the ability to model both horizontal shaking and
vertical shaking onan independent basis.
