Effect of driving long pre-stressed high-strength concrete pipe piles in alluvium and its mechanical behavior

To investigate the driving effect of long pre-stressed high-strength concrete (PHC) pipe piles on surrounding cohesive soil layers and mixed soil layers, standard penetration tests and static cone penetration tests were performed. Pore water pressure, lateral displacement in the surrounding soils and shaft forces along the piles were also measured. The process of driving piles was recorded and the mechanical behavior of the piles was researched using fibre optic sensors as well. The results indicated that significant excess pore pressure and lateral deformation were developed as the result of the pile driving and their magnitudes decreased with distance from the pile. Pile driving improved the mechanical properties of the surrounding soils and enhanced the liquefaction resistance of both the silt and silty sand layers. The ratio of soil plug length to pile length ranged from 22 to 43 % and the PHC pile with a thinner wall resulted in a greater plug. The distribution of the shaft force was nonlinear along the pile length and became more obvious with the increase of the applied load. Shaft resistance varied with the magnitude of applied load and the soil properties.