Assessing the influence of sequential basement excavation and tunneling on a pile in stiff clay: A 3D coupled consolidation approach

Urban development often necessitates underground construction activities such as basement excavations and tunneling, in close proximity to existing pile foundations supporting high-rise structures. This study investigates the combined effects of basement excavation followed by tunneling on single pile foundation in stiff clay using three-dimensional coupled consolidation numerical modelling. To ensure realistic soil behaviour, an advanced hypoplastic constitutive model for clay was employed, incorporating small-strain stiffness, and stress dependent dilatancy of soil. This research focuses on the response of single piles subjected to sequential basement excavation and tunnelling activities. A parametric study was conducted, analyzing three different basement excavation depths and three tunnel positions relative to the pile. These combinations include scenarios where the formation levels and tunnel depths are near the pile shaft (SeSt case), near the pile toe (TeTt case), and below the pile toe (BeBt case). In each scenario, the tunnel excavation was simulated after the basement excavation. The results reveal that tunnelling following basement excavation induces significant pile settlement and alters axial load redistribution along the pile, primarily due to stress release and degradation of soil stiffness. Among the three scenarios, the BeBt case exhibited the maximum pile settlement of 63.1 mm, equivalent to 7.9% of the pile diameter. The TeTt case recorded the highest induced bending moment of 328 kNm, accounting for 43.7% of the bending capacity of the pile. Additionally, the BeBt scenario resulted in the greatest deflection at the pile toe due to basement excavation. These findings provide critical insights for practitioners in assessing pile performance during sequential excavation and tunneling activities.