Vertical Load Transfer Mechanism and Function of Ultralong, Large-Diameter Grouting Piles

This study investigates the load transfer mechanism of ultralong, large-diameter cast-in-place piles before and after grouting, aiming to clarify the displacement characteristics required for full mobilization of shaft resistance in different soil layers. Three full-scale field tests were implemented on nonengineering piles (Φ = 1.8/2.2 m, L = 80/110 m) at the Anluo Yellow River Bridge project. A hyperbolic model describing τ–s and σ–s relationships under grouting effects was established, with validation performed through a MATLAB (version R2022a) program incorporating load transfer theory. The field results reveal that the displacements for full shaft resistance mobilization in fine sand changed from 4.35–26.01 mm (0.2%D–1.18%D) pregrouting to 5.27–34.05 mm (0.29%D–1.89%D) postgrouting. Corresponding values in silty clay were 3.58–25.47 mm (0.2%D–1.16%D) and 3.07–32.27 mm (0.17%D–1.79%D), while silt layers showed 7.86–14.88 mm (0.44%D–0.83%D) and 9.64–24.23 mm (0.54%D–1.35%D). The modeling further indicates that the displacement thresholds demonstrate dependency on soil properties, pile diameter, depth, and tip resistance development, with the required pile–soil relative displacement for complete shaft resistance mobilization being greater than that in shallow soil layers.