Deep Excavation Protection for Urban Underground Construction: A Case Study of an Anchored Secant Pile Wall

Abstract

Modern urban underground construction requires retaining systems that satisfy both ultimate and serviceability limit states while ensuring reliable performance throughout excavation. This study presents the numerical evaluation and performance verification of an anchored secant pile wall through the case study of the deep excavation at “Çerçiz Topulli” Square, Gjirokastra, Albania. The study involved a 12.9 m deep excavation for a three-level underground structure in multilayered soil conditions. A reproducible plane-strain finite-element model, incorporating beam-on-elastic-foundation elements, was developed to simulate staged excavation, soil stratification, groundwater conditions, anchor activation, and construction sequences. The retaining system performance was assessed using normalized wall deflection, serviceability criteria, deformation prediction accuracy, and anchor efficiency. The maximum calculated lateral wall displacement was 12.1 mm, corresponding to a normalized wall deflection (δmax/H) of 0.094%, which is substantially below the commonly accepted serviceability limit of 0.5%. Comparative analyses indicate that the prestressed anchor system reduced wall deformation by approximately 25% relative to an equivalent unanchored excavation, while controlled dewatering was required to maintain excavation stability. The proposed framework provides a validated methodology for the design verification and performance assessment of anchored secant pile walls in deep urban excavations. The findings offer practical guidance for optimizing retaining systems in multilayered soils and establish a transferable approach for similar underground infrastructure projects in complex urban environments.