Foam Rubber Modeling of the Lotung Large-Scale Seismic Experiment

Abstract

Results from a layered foam-rubber model of the Lotung Large-Scale Seismic Experiment are compared with the observed data. A Forced Vibration Test of the model predicts a peak response frequency at 4.0-4.1 hz. The actual peak response frequency of the 1/4-scale structure is 3.8 hz. Data from five earthquakes (designated, by EPRI, as events 6, 7, 8, 14, and 16) are used in this study. Events 7 and 16 are mainshocks and high-strain events; event 8 is the aftershock of event 7. Transfer functions from downhole stations to the surface for events 6, 7, 8, and 16 are compared with the corresponding transfer functions in the foam-rubber model. The foam-rubber results agree well with the observed data except for event 7 (the largest event). Transfer functions from the control motion to the top of the 1/4-scale containment for events 6, 7, 8, 14, and 16 are compared with the corresponding transfer functions in the foam-rubber model. For events 6, and 14, results of modeling using a low-strain assumption agree with the observed data. For events 7 and 16, results of modeling using a high-strain assumption agree with the observed frequency response of the containment, but the amplitudes are overestimated. For event 8, the experimental results agree well with the observed data when the high-strain assumption is used. In this study, structure response in a foam-rubber model with a stiff backfill does not support the existence of a stiff backfill at the Lotung site.