Principles of Centrifuge Modeling

A geotechnical centrifuge is used to conduct model tests to study geotechnical problems such as the strength, stiffness and capacity of foundations for bridges and buildings, settlement of embankments, stability of slopes, earth retaining structures, tunnel stability and seawalls. Other applications include explosive cratering, contaminant migration in ground water, frost heave and sea ice. The centrifuge may be useful for scale modeling of any large-scale nonlinear problem for which gravity is a primary force.
Reason for Model Testing on the Centrifuge
Geotechnical materials such as soil and rock have nonlinear mechanical properties depending on effective confining stress and stress history. The centrifuge applies an increased "gravitational" acceleration to physical models to produce identical self-weight stresses in the model and prototype. The one to one scaling of stress enhances the similarity of geotechnical models and makes it possible to obtain accurate data to help solve complex problems such as earthquake-induced liquefaction, soil-structure interaction and underground transport of pollutants such as dense non-aqueous phase liquids. Centrifuge model testing provides data to improve our
understanding of deformation and failure and provides benchmarks useful for verification of numerical models.
Value of Centrifuge in Geotechnical Earthquake Engineering
Large Earthquakes are infrequent and unrepeatable but can be devastating. This makes it difficult to obtain the required data to study their effects by post earthquake field investigations. Instrumentation of full scale structures is expensive to maintain over the large periods of time that may elapse between major temblors, and the instrumentation may not be placed in the most scientifically useful locations. Even if engineers are lucky enough to obtain timely recordings of data from real failures, there is no guarantee that the instrumentation is providing repeatable data. In addition, scientifically educational failures from real earthquakes come at the expense of the safety of the public. Understandably, after a real earthquake, most of the interesting data is rapidly cleared away before engineers have an opportunity to adequately study the failure modes. Centrifuge modeling is a valuable tool for studying the effects of ground shaking on critical structures without risking the safety of the public. The efficacy of alternative designs or seismic retrofitting techniques can be compared in a repeatable scientific series of tests.
Verification of Numerical Models
Centrifuge tests can also be used to obtain experimental data to verify a design procedure or a computer model. The rapid development of computational power over the last two decades has revolutionized engineering analysis. Many computer models have been developed to predict the behavior of geotechnical structures during earthquakes. Before a computer model can be used with confidence, it must be proven to be valid based on experimental data. The meager and unrepeatable data provided by natural earthquakes is usually insufficient for this purpose. The centrifuge is useful for verifying assumptions and improving computer models.