Numerical Modeling of Soil-Shaft Interaction Validated Using the Instrumented Hayward Bridge in California-Paper

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The study uses OpenSees to model seismic soil response and soil–shaft interaction at California’s Hayward–I580/238 bridge, assessing whether numerical analysis can support drilled-shaft seismic design when measurements are unavailable at some depths.<br /><br />Researchers developed a 30-meter free-field soil model based on data from the nearby east downhole array. They validated it against recorded ground motions from the 2018 Mw 4.4 Berkeley and 2021 Mw 3.9 San Lorenzo earthquakes. The model reproduced measured displacement time histories well, and its spectral velocity and displacement results were broadly comparable to recordings. However, it underestimated spectral acceleration, particularly for the San Lorenzo event. Uncertain soil properties—especially estimated shear-wave velocities at depths lacking measurements—may have contributed to this discrepancy.<br /><br />The validated model’s displacement histories for the Berkeley earthquake were then applied to a 12-meter drilled-shaft model with lateral soil springs representing stiff clay and weak rock. The simulated shaft’s largest displacement occurred at the ground surface, while peak soil reaction occurred about 3.5 meters below ground. The authors report maximum shaft-head deflections of approximately 3 μm in both horizontal directions.<br /><br />The results demonstrate the potential of OpenSees to estimate soil responses at different depths and analyze shaft behavior during earthquakes. The study is limited to relatively small earthquakes and an elastic shaft model; larger motions may require modeling inelastic shaft behavior. The authors also recommend refining soil and damping parameters and including vertical-direction soil springs in future work. Overall, the approach offers a useful foundation for improving seismic assessment and design of drilled shafts, subject to further validation and model refinement.

Keywords

OpenSees

seismic soil response

soil-shaft interaction

Hayward-I580/238 bridge

drilled-shaft seismic design

free-field soil model

downhole array

ground motion validation

shear-wave velocity

earthquake modeling