Centrifuge Model Tests to Identify Dynamic Properties of Dense Sand for Site Response Calculations

Four centrifuge models, tested on the large centrifuge at UC Davis, are described in this paper. These four experiments involved dense profiles of Nevada Sand (Dr = 90 to 100%) tested in two different model containers. The purpose of the experiments was to evaluate numerical site response procedures by comparison with model test data. In this paper we focus on determining basic material properties of one of the models by using in-flight measurements of shear wave velocity and calculations of stress-strain relationships using data from an extensive array of accelerometers. Shear wave velocity profiles were measured at centrifuge accelerations of approximately 10, 20, and 40 g; and before, during, and after the models were subject to base shaking using the servo-hydraulic shaker in an attempt to identify any influence of shaking history on shear wave velocity. The base shaking included realistic earthquake time histories scaled in frequency and amplitude to simulate motions with low, medium, and high intensity, and motions that included sinusoidal sweeps of different frequencies. A new windowing procedure to compute shear modulus and shear strain amplitude time histories from accelerometer array data is briefly described