Abstract: The soil in the coastal reclamation area is generally very poor, embedded with thick soft oozy soil layers. The soil can produce great consolidation settlement under the effect of late filling. Different types of surcharges have an important effect on the bridge pile foundation, and reduce the bearing capacity of pile. Balanced surcharge and unbalanced surcharge mainly affect the settlement and the horizontal displacement of pile, respectively. Combined with the Taizhou Bay bridge project construction, three piles are selected to conduct balanced surcharge loading test, and another three piles are designed to conduct unbalanced surcharge loading test to study the bearing characteristics of pile foundation under different balance surcharges. The field test results show that the negative friction of pile side is caused mainly by balanced surcharge. When the surcharge load is up to 4 m and area is 24 m×16 m, the total negative frictional resistance is up to around 2 687 kN, and the depth of neutral point is about 29.5 m, nearly being 0.36 times the pile length. The development of negative frictional resistance changes with time. The unbalanced surcharge load mainly affects the pile foundation to produce soil arching effect, and gives rises to a large horizontal displacement of pile. In the unbalanced surcharge loading test, the surcharge mainly affects the area in the range of 20 m from the ground, the maximum horizontal displacement in soil appears around 4 to 5 m off the ground, and the maximum horizontal displacement of pile appears at the top of the pile.

Key words: bridge pile foundation, unbalanced surcharge, balanced surcharge load, negative frictional resistance, soil arching effect