Seismic behavior of shallow buried water reservoirs via large scale three-dimensional numerical models

As buried water reservoirs are increasingly being utilized to store and deliver water, they are now regarded as critical infrastructures that must continue to operate in the event of an earthquake. This paper presents the results of a large-scale numerical parametric study that was carried out to advance our understanding of the seismic fluid-structure-soil interaction (FSSI) response of buried water reservoirs. Advanced nonlinear three-dimensional (3D) FSSI numerical models of reservoirs were employed while considering reservoir size, embedment depth, soil profile, and ground motion variability. The study showed that, unlike other conventional underground structures, the peak ground acceleration (PGA) has the strongest correlation to the reservoir seismic response. Increasing the embedment depth or reservoir size was found to generally increase the demands on the structural elements while reducing the base and backfill slippage. Softer sites were found to cause an increase in the roof racking and including the vertical component of the motion increased the water dynamic pressures. Among the columns, the ones closest to the center were found to experience the highest demands and the ones at the corner the lowest. In fact, in some extreme cases, a total collapse of the reservoir was initiated by column failure due to the lack of structural redundancy. The roof in-plane shear stresses were observed to accumulate near the walls, indicating a diaphragm behavior. The reservoir's unique seismic response compared to other underground structures makes generalizing the commonly used simplified design procedures inapplicable. Instead, 3D FSSI numerical models were demonstrated to be a reliable tool for the seismic design of buried reservoirs.