Determination of Soil Properties for In-Flight Models Using Bender Elements

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One method to simulate approximately the effects of earthquake loading on a full-size earth structure, such as an earth dam or a retaining wall, is to shake a physical model of the soil structure in-flight on a geotechnical centrifuge. The various physical simulation methods available are all approximations to reality, and it is important to understand clearly what these approximations are.Data from centrifuge experiments can be used to study the physical mechanisms involved in complex problems, as well as to verify numerical procedures, and to evaluate new design approaches. However centrifuge modeling is a complex experimental method. There are some uncertainties in modeling techniques that need further study so as to establish confidence in the accuracy of the simulation. One of the most significant uncertainties involves the soil properties in a model during the flight (rotation) of the centrifuge. It has been accepted practice to measure the properties prior to or after flight, which can be significantly different from the properties that exist during flight. It is also generally assumed that the soil samples are uniform and isotropic, basically because of the difficulty in measuring the actual degree of uniformity and isotropy. There are other approximations, which also need to be examined.The principal investigator is addressing the accuracy of the simulation by using "bender" elements (a relatively new technique) to measure the shear modulus of soil. This is a very promising approach that is expected to lead to an improved understanding of the approximations inherent in simulating on a centrifuge the earthquake loading on an earth structure.