CONSIDERATIONS FOR DEFORMATION ANALYSES FOR SUBDUCTION ZONE EARTHQUAKE LOADINGS

摘要

Recent global seismic events and a better understanding of subduction zone behavior have placed an increased emphasis on analyzing the effects of long duration shaking on earth embankments. Analytical tools that have largely been developed with shorter events in mind may not accurately account for the effects of long duration shaking. When analyzing long duration shaking within the finite difference framework of FLAC, force imbalances due to large deformations are magnified by long duration loading records, leading to unrealistic deformations and misleading results. With large deformations that can accompany long duration shaking, the mass within the model is redistributed such that initial static reaction forces may not reasonably balance the deformed mass. Additionally, reservoir pressures calculated for the undeformed embankment may not accurately represent the pressures that should be applied to the deformed embankment. These phenomena lead to force imbalances that can cause significant distortion of the model. This distortion is increased when the unbalanced forces act over the extended time associated with subduction zone loadings. Even when incorporating an increased bedrock thickness in the model, significant distortion may remain for long duration loadings. Using FLAC’s internal programming language, an approach was developed to update reservoir pressures and reaction forces that significantly reduces the force imbalance and mitigates the effects of any remaining unbalanced forces. The force updating routines recalculate correct reservoir pressures and reaction forces associated with the constantly deforming model. After correctly accounting for these forces, the increased confidence in the results can lead to more economical designs.