Liquefaction-Induced Settlement and Pile Foundation Performance in Gölbaşı after the 6 February 2023 Kahramanmaraş Earthquakes: A Numerical and Site Observed Case Study

The 6 February 2023 Kahramanmaraş earthquake sequence caused widespread structural damage and ground failure across southern Türkiye. Gölbaşı district, Adıyaman province, was among the most affected localities, underlain by young alluvial, lacustrine, and marsh deposits with a shallow groundwater table. This paper presents a case study of the damaged Gölbaşı Muftiate Building, a mat-founded structure on an unconnected ground-improvement pile system that underwent severe settlement and tilting after the earthquakes. The study integrates post-earthquake field observations, SPT and CPT data, laboratory characterization, strong-motion record selection, one-dimensional site-response analysis, pile-soil interaction analysis, two-dimensional finite-element modelling, and a simplified CPT-based liquefaction settlement assessment. The idealized profile comprises silty sand (0–8.0 m), soft clay (8.0–11.5 m), sandy silt (11.5–16.5 m), and hard clay below 16.5 m, with liquefaction-prone units in the silty sand and sandy silt layers. DEEPSOIL analyses indicate excess pore-water-pressure generation and free-field horizontal deformation under the selected record. RSPile results show liquefaction increases pile displacement, bending moment, and shear demand several-fold relative to non-liquefied conditions. Plaxis 2D simulations reproduce settlement consistent with field-observed damage and confirm excess pore-pressure development in the upper profile. A simplified calculation yields a median liquefaction-induced settlement of about 1.11 m, consistent with the observed one-meter building settlement. These results show that piles terminating within or near liquefiable layers may lose effectiveness when lateral spreading, cyclic mobility, and post-liquefaction reconsolidation occur together. The case underscores the need for integrated liquefaction triggering, deformation, and pile-performance assessments in seismic foundation design.