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Liquefaction Mitigation with Displacement Rigid Inclusions
Rigid inclusions are a ground improvement technique consisting of introducing continuous, vertical elements to increase vertical stiffness and mitigate settlement of soils under load. In the United States, most rigid inclusion projects appear to involve drilled, grouted displacement elements using displacement augers. Displacement rigid inclusions significantly change the properties of the surrounding soil; they improve the strength and stiffness of granular soils due to densification and increasing lateral stresses, and cause displacement, shearing, and consolidation of saturated fine-grained soils. The beneficial effects of installation on the mechanical properties of soil are often ignored during design analyses, mostly due to the difficulty in evaluating post-installation soil properties and in assessing their effect on rigid inclusion performance in a reliable, repeatable way. Ignoring the improvement of mechanical properties of the soil due to installation can yield overly conservative designs. This paper presents a case history where significant densification of a liquefiable granular layer was accomplished through installation of rigid inclusions. The liquefaction potential of the site was assessed through numerous pre- and post-installation cone penetration test (CPT) probes. Comparison of the estimated pre- and post-installation values of factor of safety against liquefaction in the granular layer reveals increases in the factor of safety from an initial range of 0.75−1.0 to values greater than 1.3. Such level of improvement, which is consistent with findings from other authors, is a strong indicator that rigid inclusions are an effective measure to mitigate liquefaction and to upgrade seismic site classification of a site with a liquefiable soil profile. This paper discusses details of the project, site characterization, and liquefaction assessment. It also briefly discusses the mechanics of soil improvement around rigid inclusions, potential limitations and under-conservatism of current post-installation liquefaction assessment methods, and simple hand calculations methods to predict degree of soil densification.
Liquefaction Mitigation with Displacement Rigid Inclusions
Rigid inclusions are a ground improvement technique consisting of introducing continuous, vertical elements to increase vertical stiffness and mitigate settlement of soils under load. In the United States, most rigid inclusion projects appear to involve drilled, grouted displacement elements using displacement augers. Displacement rigid inclusions significantly change the properties of the surrounding soil; they improve the strength and stiffness of granular soils due to densification and increasing lateral stresses, and cause displacement, shearing, and consolidation of saturated fine-grained soils. The beneficial effects of installation on the mechanical properties of soil are often ignored during design analyses, mostly due to the difficulty in evaluating post-installation soil properties and in assessing their effect on rigid inclusion performance in a reliable, repeatable way. Ignoring the improvement of mechanical properties of the soil due to installation can yield overly conservative designs. This paper presents a case history where significant densification of a liquefiable granular layer was accomplished through installation of rigid inclusions. The liquefaction potential of the site was assessed through numerous pre- and post-installation cone penetration test (CPT) probes. Comparison of the estimated pre- and post-installation values of factor of safety against liquefaction in the granular layer reveals increases in the factor of safety from an initial range of 0.75−1.0 to values greater than 1.3. Such level of improvement, which is consistent with findings from other authors, is a strong indicator that rigid inclusions are an effective measure to mitigate liquefaction and to upgrade seismic site classification of a site with a liquefiable soil profile. This paper discusses details of the project, site characterization, and liquefaction assessment. It also briefly discusses the mechanics of soil improvement around rigid inclusions, potential limitations and under-conservatism of current post-installation liquefaction assessment methods, and simple hand calculations methods to predict degree of soil densification.
Liquefaction Mitigation with Displacement Rigid Inclusions
Gómez, Jesús (author) / Nodine, Mary (author) / Burton, Elgin (author)
International Foundations Congress and Equipment Expo 2024 ; 2024 ; Dallas, Texas
IFCEE 2024 ; 306-314
2024-05-03
Conference paper
Electronic Resource
English
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