Abstract: The loading and deformation behaviors of the large-diameter belled piles are different from and similar to those of straight large-diameter piles, because of their enlarged tip. Similar to the large-diameter bored piles the large-diameter belled piles have size effect, and but an increase of the ratio of the enlarged tip diameter to the shaft diameter. According to the test data, the load and deformation behaviors of large-diameter bored piles with different ratios of the enlarged tip diameter to the shaft diameter are analyzed, and the relationship between the tip resistance and the settlement is studied. Finally, the size effect coefficient of the large-diameter belled piles is proposed.