A FIELD-CALIBRATED NUMERICAL–EMPIRICAL FRAMEWORK FOR DEEP EXCAVATION DESIGN IN SOFT ALLUVIAL SOILS OF İZMIR, TÜRKIYE

In densely populated urban environments, deep excavations in soft ground present critical geotechnical challenges due to high groundwater table and weak cohesive soils. Diaphragm walls supported by struts or tieback anchors are frequently used to stabilize such excavations, yet predicting deformation behavior remains complex and highly site-dependent. This study evaluates the performance of four deep excavation projects in İzmir, Türkiye, where excavation depths reached up to 17 meters within soft to medium alluvial deposits.A performance-based back-analysis methodology is implemented, where numerical models are calibrated using field-monitored inclinometer data. A non-linear soil constitutive model with stress-dependent stiffness and hardening behavior is employed, and the elastic stiffness modulus (E₅₀) is iteratively adjusted to reflect actual wall displacements. A site-specific empirical correlation is developed between E₅₀ and SPT-N₆₀, resulting in a power-law model with strong predictive capability for local soil conditions.Findings demonstrate that conventional empirical stiffness correlations often fail to capture the deformation response of deep excavations in İzmir's geologic setting. The calibrated models offer improved insight into wall-soil interaction and enhance the reliability of deformation predictions. The study promotes a practical framework integrating numerical modeling with field monitoring for safer, performance-based design in soft urban ground.