Liquefaction, Building Response, and Seismic Settlement Mechanisms in the Adapazarı Basin

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Yılmaz D.

Black Sea Journal of Engineering and Science, cilt.9, sa.2, ss.812-825, 2026 (TRDizin)

Özet

The 17 August 1999 Mw 7.4 Kocaeli earthquake caused widespread settlement of buildings in downtown Adapazarı, although clear surface evidence of free-field liquefaction was limited. This study investigates the mechanisms responsible for these settlements by integrating nonlinear site response analysis, liquefaction assessment, and foundation-level deformation modeling. Because the main shock was not recorded in the city center, ground motions were estimated using nonlinear site response analyses performed with the D-MOD program and calibrated against recorded aftershocks. The resulting peak ground acceleration in downtown Adapazarı was estimated to be approximately 0.30 g. Simplified free-field liquefaction analyses predicted liquefaction in shallow silty and sandy silt layers between depths of 1.5 m and 4.0 m. However, strain restriction enforced by a stiffer surrounding soil matrix, which restricted the formation of shear strain in potentially liquefiable strata, is responsible for the lack of broad free-field manifestations. Localized liquefaction beneath shallow foundations resulted from structural reaction effects that greatly increased cycle stress ratios beneath buildings, especially for short-period structures. Liquefaction-induced volumetric strains account for approximately 40–50% of the observed settlements. The remaining settlement is explained by lateral sliding of supporting soils once seismic bearing capacity was exceeded, as evaluated using simplified Newmark-type sliding block analyses. The findings demonstrate that building settlements in Adapazarı resulted from the combined effects of soil stratigraphy, structural response, and foundation-level deformation, highlighting the limitations of free-field liquefaction procedures for urban settings.