In this study, field monitoring and numerical investigation were carried out to investigate the effects of reclamation on long piles (146 m) with large diameters (3.4 m). The surface settlement, subsurface horizontal displacement, and pore water pressure were recorded during the field monitoring experiment. Numerical back analysis was carried out to investigate the behavior of the pile response to reclamation works. The field monitoring data and numerical analysis revealed that the east dam and middle dam underwent notable settlement after their construction. After 12 months, the maximum measured settlement of the east dam was 561 mm. The soil on both sides of the east dam moved away from the dam during the reclamation. The horizontal displacement of soil on both sides of the dam was approximately symmetrical with respect to the dam. The maximum horizontal displacement of the pile was calculated as 3.8 mm, which is substantially lower than the limit suggested by the Chinese Specifications for Design of Foundation of Highway Bridges and Culverts and the Canadian Foundation Engineering Manual. The maximum axial force of pile after reclamation of RS area decreased by 37% compared with that upon the completion of pile. In contrast, the maximum axial force along pile increased by 20% due to reclamation of RN area.