Japanese Geotechnical Society Special Publication
Online ISSN : 2188-8027
ISSN-L : 2188-8027
Liquefaction mitigation 1
Seismic coupling of structures on liquefiable and mitigated sites with drainage and ground densification methods
Yu-Wei HwangShideh Dashti
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2024 Volume 10 Issue 45 Pages 1671-1676

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Abstract

Over the past years, ground densification and soil drains have been commonly used as countermeasures against the consequences of seismic soil liquefaction. However, the state-of-practice for designing such mitigation methods is typically for free-field conditions, without considering seismic soil-structure interaction (SSI) or structure-soil-structure interaction (SSSI). In this paper, three-dimensional (3D), fully-coupled, nonlinear finite element analyses, validated with centrifuge experimental results, are used to evaluate how the mitigation mechanism (e.g., densification, enhanced drainage, or their combination) affects the seismic performance of adjacent, similar and dissimilar, inelastic, shallow-founded structures on liquefiable sites. A combination of densification with enhanced drainage under and around the entire footing is shown as the most effective strategy to notably reduce the mitigated foundation’s permanent settlement and tilt (although not always to acceptable levels), regardless of building spacing. Enhanced drainage alone may reduce foundation’s average settlement, but it does not necessarily reduce tilt when near another structure. For the conditions evaluated, the presence of either mitigation method under one structure is shown to notably amplify the permanent tilt and possibly the flexural deflections of its unmitigated neighbor at shorter spacings (S < W/3 where S is the edge-to-edge building spacing and W is the building width), while having a minor impact on its settlement. The results indicate that mitigation (either densification, enhanced drainage, or their combinations) must be designed with extreme care in urban environments, with the goal of improving the overall performance at a systems level for the building as well as its surrounding structures.

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