The 1999 Kocaeli Earthquake (M=7.4) caused significant damage along Izmit Bay. We investigated the performance of improved soil sites in the region. An important site was Canefour Shopping Center which is underlain by soft clays, silts, and liquefiable sands. Jet-grout columns had been installed to reduce static settlements and prevent liquefaction. Post-earthquake inspections showed the grouting to be effective in reducing damage. Dynamic finite element analyses were used to model the reinforced ground at the site. Surprisingly, the results suggest that the columns did not reduce seismic shear stresses and strains in the soil mass. Column effectiveness was more related to vertical support that prevented settlements. Our findings imply that design methods that assume composite shear behavior for columnar-reinforced ground can greatly overestimate the actual level of improvement.
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