Bearing capacity of piles with negative skin friction based on field tests

• Two PHC pipe piles with different pile - end bearing layers (end - bearing and friction piles) were tested to compare NSF distribution patterns. • Two working conditions (no pile - top load and applied working load) were simulated, showing dynamic neutral - point migration. The maximum dragload occurred at the neutral point under no load, and the neutral point shifted upward under working loads. • Constructing piles after foundation treatment effectively reduces dragload, providing empirical evidence for optimizing construction sequencing. These results fill critical gaps in understanding the effects of pile - end conditions, loading scenarios, and construction timing on NSF and offer practical guidance for pile design in deep soft soil regions. The coastal regions of China possess extensive deep layers of soft soil. Consequently, post-construction settlement inevitably induces negative skin friction on pile foundations. The dragload generated in an zone that is affected by negative skin friction above the neutral point can significantly reduce the bearing capacity of the pile foundation. At present, accurate analytical methods for assessing the bearing capacities of pile foundations subjected to negative skin friction are lacking. In this study, two prestressed high-strength concrete pipe piles with different pile-end bearing layers were tested. Two working conditions (i.e., no load applied to the pile top and a working load applied to the pile top) were simulated to study the variation in the negative skin friction of the pile foundations. When no load was applied to the pile top, the axial force at the neutral point was the maximum dragload on the pile shaft. When a working load was applied to the pile top, the neutral point shifted upward. Hence, constructing a pile foundation after foundation treatment effectively reduced the dragload. These results provide a basis for calculating and designing the negative skin friction and estimating the load-bearing capacity of pile foundations in coastal regions with deep soft soils.