Study On Bearing Behavior Of Single Pile Under Horizontal And Downward Loads

Pile foundation is widely used in high-rise and super high-rise buildings,ports,bridges and other projects.Under complex working conditions,the pile top will bear the combined load formed by downward and horizontal load,and the vertical and horizontal load are often not applied at the same time.How the application sequence of the downward and the horizontal load affects the internal force of the pile,the frictional resistance of the pile and the resistance of the soil layer is a difficult problem in the pile foundation design under the combined load.Based on the model tests and numerical analysis,the importance of studying the internal force of pile,friction resistance around the pile and soil layer resistance under the combined load of vertical and horizontal load is demonstrated.The research results on the vertical bearing behavior of single pile with pre-applied horizontal load show that horizontal load applied firstly will increase the settlement of pile head to a certain extent,but it has little effect on the vertical failure load.As far as the internal force of a single pile is concerned,pre-application of lateral load will add the frictional resistance of the facing soil surface of the pile and reduce the frictional resistance of the back soil surface within the range of 0 ~ 15 d below the ground,which generally indicates that the average frictional resistance of the pile is diminished.At the same time,the pre-applied horizontal load will heighten the bending moment,and the amplitude is positively related to the pre-applied lateral load.In addition,pre-application of horizontal load will enhance the soil resistance in the surface which is facing the soil of pile,but has no significant effect on the soil resistance of pile in the surface backing the soil.What should be pointed out is that horizontal load applied in advance and vertical load applied secondly of a pile,the lateral load will significantly raise the shear force of the pile,and the effect is usually ignored in pile foundation design.The results on the lateral bearing behavior of a single pile subjected to vertical load indicate that the horizontal displacement and bending moment of the pile in the range of 0 ~ 10 d below the ground will be decreased by applying downward load firstly,thus improving the horizontal failure load of the pile.Furthermore,the downward load plays a major role in the friction,while the horizontal load has little effect on it.In addition,the pre-applied downward load has little influence on the transmission mode of bending moment,the maximum bending moment and the location of the first zero point of bending moment of the pile,and the pile-soil separation range on the backing soil surface of the pile is less affected by the vertical load.According to the research of single pile with downward load applied in advance and horizontal load applied subsequently,a simple method to estimate the maximum bending moment of pile under vertical and lateral combined load is proposed,and the rationality of the method is verified.