In order to understand the piles with expanded diameter perfectly and to widen their actual application, the bearing behaviors was studied and load-settlement curves (that is Q-s curves) were obtained for piles with expanded diameters. It was found that the shapes of Q-s curves change slowly, and the damage of piles was in the form of shear damage of the soil under the branch and the penetrating damage of the soil under the pile end. Q-s curves of the 3 field testing piles were well fitted by the power-hyperbola combined mathematical model, and the correlativity coefficients R was over 0.9997, better than the power function model or the hyperbola model. The fitting equation from the former 11 groups of testing data of a pile was used to forecast the load of the other 4 groups, and prediction was good. The relative error between the prediction value and the actual measurement was
61485;0.26%―1.32%. So it is can be concluded that the power-hyperbola combined mathematical model is appropriate to describe Q-s curves of piles with expanded diameters.