Based on the ultimate uplift bearing capacity tests of the enlarge base piles in Tianjin Yujiabao South Underground Garage Project

the uplift bearing behavior

the uplift failure mode and the bearing mechanism of the enlarged base piles is analyzed by numerical simulation. The results show that the ultimate uplift bearing capacity of the enlarge base pile with the increase of 8.5% of concrete material

increases about 50% more than the uniform section pile; the ultimate bearing capacity is significantly improved by the soil around the enlarged base. When the loading is small

the uplift resistance is mainly provided by the shaft fiction of the uniform section part of the enlarged base pile; the ratio of the uplift resistance of the enlarged base to the loading on the pile top increases approximately linearly with the loading increase. The shear failure firstly occurs in the pile-soil interface of the uniform section part with the loading increase; then the compression failure of the soil around the enlarged base occurs

and the uplift resistance reaches the ultimate bearing capacity. The ultimate uplift resistance of the enlarge base of the different length piles is almost the same when the enlarged bases are located in the same layer of soil; and the uplift bearing efficiency reduces as the pile length increases. The uplift resistance of the enlarge base is composed of the dead weight

the vertical component of the normal force and the shaft friction; the vertical component of the normal force provides the major uplift resistance of the enlarged base

the percentage of the total uplift resistance of the enlarged base is about 70%.