Study On Vertical Bearing Characteristics Of Pile Foundation Of Existing Bridge Under Scouring

Scouring is one of the main causes of bridge collapse and destruction.For some large cross-sea bridges,the foundation piles are in a complex water flow environment for a long time.The water flow scour will take away the soil material around the piles,which will increase the exposed length of the foundation piles and reduce the buried depth of the piles,resulting in the change of the bearing characteristics of the bridge pile foundation.Although there are many researches on the scour problem of bridge pile foundation,the research on the influence of scour on the vertical bearing behavior of bridge pile foundation is relatively rare,so it has been highly valued by many scholars.How to analyze the change of vertical bearing characteristics of existing bridge pile foundation after water scour is an urgent problem to be solved in bridge pile foundation.In this paper,the influence of scouring on the vertical bearing characteristics of single pile and pile group foundation is studied.The main work is as follows:(1)For the scour problem of single pile,a nonlinear analysis method of vertical bearing characteristics of existing bridge pile foundation under scour condition is proposed.Based on the load transfer method and the finite difference method,a nonlinear simplified analysis method for the vertical bearing characteristics of in-service bridge pile foundation under scouring conditions is established by considering the soil rebound caused by the scouring and unloading of the soil around the pile and the change of the ultimate friction resistance of the pile side and the ultimate end resistance of the pile end.The correctness of the simplified method is proved by comparing with the finite element results,and the vertical bearing performance of the in-service bridge pile foundation under scouring conditions is calculated and analyzed.The results show that the scour will reduce the ultimate bearing capacity of the pile,and then reduce the safety factor of the pile.Soil rebound caused by scouring has a great influence on the bearing characteristics of pile under working load.The variation law of pile top displacement with scour depth under working load is related to pile size and stratum conditions.In practical engineering,the results should be considered comprehensively to obtain the results consistent with the actual situation.(2)For the scour problem of pile group,the influence of scour depth,pile spacing,pile slenderness ratio and soil conditions on the bearing characteristics of piles at different positions after scour is studied.The results show that the pile top of the foundation pile is rebounded at different scour depths.With the increase of scour depth,the rebound amount of the pile top increases,and the ability of the middle pile to share the upper load gradually increases.With the increase of pile spacing,the force acting on the corner pile gradually transfers to the side pile and the middle pile.The short pile is closer to the end bearing pile,while the long pile is closer to the friction pile.In the actual engineering design,special attention should be paid to the environment of the pile end bearing layer of the short pile and the characteristics of the soil around the long pile.Through the study of the above problems,we have a deeper understanding of the change of the vertical bearing characteristics of the foundation pile caused by the scour,and deepen the understanding of the bridge scour problem.The results obtained can also provide reference for others to analyze the scour problem of bridge pile foundation.