Depth-Dependent Load-Transfer Variability in Three Ultralong Bored Piles: Evidence from Full-Scale Load Tests

Ultralong postgrouted bored piles constructed with the same design configuration may exhibit different internal load-transfer behaviour that is not fully reflected by pile-head load–settlement curves. This study reanalysed full-scale maintained-load tests on three 108.9-m-long bored piles using vibrating-wire gauges, distributed fibre-optic sensing (DFOS), and settlement-rod measurements. Inter-pile variability was evaluated by directly comparing SYZ2 and SYZ3 under first formal loading, while the first loading and reloading of SYZ1 were analysed separately to assess loading-history effects. At 30 MN, SYZ3 showed shallower axial-load transfer than SYZ2, with the z75, z50, and z25 elevations 8.80–10.81 m shallower and less axial force remaining at the prescribed shaft-grouting elevation. SYZ1 exhibited a marked reduction in pile-head settlement during reloading, while the depthwise shaft-resistance pattern remained broadly similar. These results show that similar pile-head responses do not necessarily indicate similar internal load-transfer states. Continuous internal monitoring therefore provides important complementary information for evaluating load-transfer variability and the depthwise response of postgrouted ultralong bored piles.