Seismic Interactions Among Multiple Structures on Liquefiable Soils Improved with Ground Densification

Abstract

Current guidelines for evaluating the performance of ground densification as a liquefaction countermeasure near buildings are based on free-field conditions. However, particularly in urban areas, where structures are constructed in the vicinity of each other, structure-soil-structure interaction in liquefiable deposits near two adjacent buildings (SSSI2) and multiple buildings (?3) in a building cluster (SSSI3+) have been shown to be consequential on key building engineering demand parameters (EDPs). Yet, their potential tradeoffs associated with ground densification are currently not well understood. In this paper, three-dimensional, fully-coupled, nonlinear, dynamic finite element analyses, validated with centrifuge models of SSSI2, were used to explore the influence of ground densification and the building spacing to width ratio (S/W) on key EDPs of buildings experiencing SSSI2 or SSSI3+ (particularly for four structures in a square-shape configuration). For the conditions considered, ground densification reduced the permanent settlement of an isolated structure by up to 58% compared to a similar unmitigated structure. Both SSSI2 and SSSI3+ had a minor impact on the mitigated structures’ average settlement compared to SSI. In contrast, SSSI2 and SSSI3+ strongly amplified the permanent tilt of the mitigated structure by up to 6.5 times compared to SSI at S/W?<?0.5, due to the enhanced degree of asymmetry in the properties of and demand on the underlying soil. Increasing spacing reduced the permanent tilt of structures under SSSI2 or SSSI3+. Overall, the results suggest that SSSI2 and SSSI3+ can adversely affect the foundation performance and hence, damage potential of the mitigated soil-foundation-structure system compared to SSI, particularly at S/W?<?0.5. Such complexities need to be considered in mitigation planning and design of urban structures.