Study On Coupled Bearing Mechanism Of Pile Foundation Under Vertical And Horizontal Combined Load

In addition to the vertical loads,the pile foundations supporting the marine structure are also subjected to the lateral loads such as wind,wave and current load from the marine environment.The p-y and t-z curves methods,which are widely used in practical engineering,are independent of each other.The response of pile foundation under combined load is different from that under pure horizontal load or pure vertical load.In the case of combined loading pile,the horizontal load affects the vertical response of pile foundation,and the vertical cyclic load reduce the confining pressure.Therefore,it is necessary to study the coupled bearing mechanism of pile foundation under combined load.The p-y and t-z methods are improved based on the existing theory and the coupled bearing behavior of pile foundation under combined load is studies in this paper.Firstly,the coupled pytz model is developed.The traditional p-y model is improved in this paper.According to the distributed spring model,the passive and active lateral soil resistance of the pile side during the process of horizontal loading is obtained,which is coupled to the vertical bearing t-z model to realize the coupling of p-y and t-z.The pile element is connected with p-y and t-z element by rigid beam model to reasonably simulate the additional moment effect of vertical friction on pile side thus realizing The pytz model of coupling horizontal load to vertical bearing behavior.Then,the influence of horizontal load on the vertical bearing characteristics of pile foundation is studied.Based on the proposed coupled pytz model,a coupled pile-soil model is established and verified by exiting centrifuge experiments.The coupled bearing mechanism of pile foundation under combined vertical and horizontal loads is analyzed,including different horizontal load levels,bending moments and pile slenderness ratio.The results show that,compared with the pure vertical load,the vertical bearing capacity of the pile foundation increases by 5.7%,19.2% and 37.9% when the horizontal load is 1.0 MN,2.0 MN and 3.0 MN,respectively.Finally,the influence of friction fatigue on p-y curve of pile foundation under vertical cyclic load is analyzed.According to the t-z degradation model under vertical cyclic load,the p-y model of vertical skin friction degradation under vertical cyclic load is developed to realize the coupling effect of t-z on p-y.And the influence of vertical cyclic load on horizontal bearing capacity of pile foundation is analyzed.The results show that due to the degradation of horizontal pressure caused by friction fatigue.As a result,the lateral bearing capacity of pile foundation is reduced,and the p-y curve also degenerates with the vertical cycle load.The degradation mainly occurs in the previous cycles.With the increase of cycles,the reduction degree of lateral soil resistance slows down.