Seismic Performance of Underground Reservoir Structures: Insight from Centrifuge Modeling on the Influence of Backfill Soil Type and Geometry

Abstract

The seismic response of underground reservoir structures is a complex soil–structure interaction problem that depends on the properties of the earthquake motion, surrounding soil, and structure. More experimental and field data of the response of these structures under different boundary conditions are needed to validate analytical and numerical tools. This paper presents the results of four centrifuge experiments that investigate the seismic performance of reservoir structures, restrained from rotational movement at their roof and floor, buried in dry, medium-dense sand and compacted, partially saturated, silty sand. This study focuses on the influence of backfill soil properties, cover, and slope on accelerations, strains, lateral distortions, and lateral earth pressures experienced by the buried structure. The structure to far-field acceleration spectral ratios were observed to approach unity with added soil confinement, density, and stiffness. Both dynamic thrust and accelerations on the structure showed a peak near the effective fundamental frequency of the backfill soil. The addition of a shallow soil cover and stiffness slightly increased seismic earth pressures and moved their centroid upward, hence slightly amplifying seismic moments near the base. The added stiffness, density, and apparent cohesion of the compacted site-specific soil did not influence the magnitude of dynamic earth pressures significantly but often moved their centroid upward. A sloping backfill reduced the earth pressures and bending moments near the top of the wall because of the reduced soil mass. The trends in the experimental results indicate that new analytical procedures and design guidelines are needed to account for the backfill soil conditions and ground motions for which these underground structures must be designed.