Abstract: The behaviors of the large diameter belled concrete piles with manual digging are studied based on field tests and numerical analysis of a pile foundation poject. The horizontal capability and deformation of the large diameter belled concrete pile is analyzed based on the measured results of displacement, moment and internal force of piles. Belled tip, the important factor, is analyzed for horizontal bearing properties. Using FLAC3D, the test results are simulated, and the reasonable factors are studied. The results show that the large diameter belled pile is a rigid pile, the stress and strain on the pile gradually increase as the load increases, and the bending on the pile nonlinearly increases. The bending will reach the maximum at the pile where under the top twice diameter of the pile, and the enlarged pile cap is under a lot of moment. The belled tip also bears much bending.