3D Analysis of Short Floating Pile Response to Adjacent Excavation: Geometric and Cross-Sectional Effects in Soft Clay

Deep excavations in urban soft clay soils pose stability risks to adjacent pile foundations. This study presents a three-dimensional coupled mechanical–fluid numerical analysis of long-term interactions between deep excavations and adjacent short floating circular and X-shaped concrete core (XCC) piles in soft clay. Using a validated finite difference model, a parametric study examined excavation depth, pile location, excavation rate, pile geometry, pile head boundary conditions, and initial working load on pile behaviour over 2000 days. Results show that pile geometry significantly influences pile response when piles are located within the first two-thirds of the primary influence zone (PIZ), particularly when excavation depth exceeds 0.67Lₚ. XCC piles experience greater settlements than circular piles, with the maximum differences at locations corresponding to the peak ground surface settlement. Pile tilting was greatest adjacent to the excavation wall, decreasing to minimum values at approximately 0.75–0.8He for both pile types. Excavation rate effects are most significant within the PIZ, with slower rates causing greater pore pressure dissipation. XCC piles develop larger bending moments than circular piles under all head boundary conditions, particularly when pile toes are close to the final excavation level. Long-term settlement and tilting are governed primarily by soil consolidation.