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Liquefaction Risk Mitigation using Jet Grouting Cells
Trevi Group has been involved in the design-build of a commercial building in Turkey in an area prone to liquefaction. The foundation of the building is located approximately 10 m below original grade, which still leaves about 10-12 m of potentially liquefiable sand underneath the bottom slab.
The owner proposed creating a grid of jet grouting cells—a common technique to improve liquefaction resistance in soil—with a spacing of 5 m by 5 m. The material confined inside the cells would be subject to much less shear strain than under free field (natural) conditions, thereby minimizing the risk of soil liquefaction.
Trevi wanted to investigate the efficacy of larger cell dimensions in order to optimize project cost and to reduce construction time. Itasca was asked to perform numerical analyses to assess the performance of bigger cells, such as 7 m by 7 m and 10 m by 10 m.
Itasca a) interpreted the soil investigation (in particular Cone Penetration Tests) to obtain significant parameters necessary for the numerical analyses; b) evaluated the liquefaction potential and depth using numerical analyses*; and, c) analyzed free field conditions, a 5 m by 5 m grid (the original design), a 7 m by 7 m grid (an alternative optimized solution proposed by the contractor), and a 10 m by 10 m grid (the upper limit considered for this location of the project site).
*The Finn-Byrne constitutive model was adopted correlating the C1 parameters to Relative Density obtained from CPT tests.
The numerical analyses indicated that there would be no significant difference between the three grid sizes investigated. Therefore, the 7 m by 7 m grid (to be conservative) proposed by the contractor was approved by the owner, resulting in both cost savings and reduced construction time.