In-Ground Gravel–Rubber Panel Walls to Mitigate and Base Isolate Shallow-Founded Structures on Liquefiable Ground

Abstract

The effectiveness of a new liquefaction mitigation strategy is investigated experimentally for newly constructed shallow-founded structures: an in-ground gravel–rubber (GR) panel wall system. The goal was to limit the negative consequences of liquefaction in terms of permanent seismic deformation, while benefiting from the positive consequences of liquefaction in terms of base isolation. The influence of GRs was systematically evaluated in the centrifuge on the seismic performance of a layered liquefiable deposit in the far-field and near two different model structures. The structures represented the key properties of a 3-story building (Structure A) on a 1-m thick mat foundation and a 9-story building (Structure B) with a 1-story basement. The performance of Structure A with GRs was also compared with a similar structure without mitigation and with conventional mitigation strategies that either enhanced drainage alone (e.g., prefabricated vertical drains) or increased shear stiffness around the foundation’s perimeter (e.g., structural walls). Test results showed that the GR wall system could greatly improve the overall seismic performance of short-period structures like A, but may be detrimental to long-period structures like B. The GRs below Structure A effectively isolated the total system, reducing average and differential settlements below the foundation (although not necessarily to acceptable levels), while also reducing the seismic demand transferred to the superstructure, a combination rarely observed by conventional mitigation strategies. The same GR system under Structure B experienced greater seismic moments and shear stress, inducing large shear deformations in soil that led to this structure’s significant rotation and flexural deflection. The foundation continued to rotate even after shaking because of P-Δ effects, resulting in its overturning failure. These results show that GR systems can be quite effective for low-rise structures, but additional reinforcement may be necessary to reduce foundation tilt. Use of such mitigation measures under taller and heavier structures must be accompanied with great caution. Despite their practical limitations, evaluation of GR panel walls may guide future developments of combined, economical, and sustainable mitigation strategies that improve the overall performance of the soil–foundation–structure system.