Upgrading the National Geotechnical Centrifuge

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This action is to provide funds for the construction of an enclosure to the National Geotechnical Centrifuge. Centrifuge modeling is a useful tool for studying a wide variety of geotechnical earthquake engineering problems. The state of stress and strain in an earth structure is dependent upon the overburden pressure, which is analogous to the hydrostatic pressure which increases with depth in a body of water. This overburden pressure is a result of gravitational loading. When testing a scale model of an earth structure, this gravitational loading must be correctly scaled, and this requires that gravity be increased in proportion to the reduction in the scale of the model: a half-scale model has to be subjected to twice the normal gravity loading. This increase in gravity loading can be obtained by testing the scale model in a centrifuge. The National Geotechnical Centrifuge was donated by NASA AMES to the University of California at Davis. It has been converted for use as a geotechnical engineering centrifuge, and more recently it was moved to the Davis campus. It is now operational at the new location, but funds were not available to provide a roof for the enclosure. As a result, the centrifuge is operating in the open air, which severely limits the capacity of the machine due to windage losses: as the arm turns it acts as a large centrifugal fan. These windage losses are unavoidable, but they can be reduced significantly by appropriate design of the enclosure. For the National Geotechnical Centrifuge, the open pit installation performance can be increased from 100 g-tons to 500 g-tons by installing a suitably designed enclosure. The increased performance provides a capacity which is sorely needed in the United States. Researchers needing this capacity must currently perform their tests on a centrifuge in Cambridge, England. This is both costly and slow. The construction of an enclosure for the National Geotechnical Centrifuge will provide a facility that will increase dramatically the experiments that can be performed in geotechnical engineering, in particular in earthquake engineering.