Analysis Of Bearing Characteristics Of Bridge Pile Foundation Under Vertical Load

Widely applied in bridge engineering,pile foundation must provide adequate bearing capacity when enduring vertical load.Its settlement value should be controlled to meet the vertical deformation limit as required by the superstructure.In order to ensure the safe operation of bridge,it requires profound study on vertical bearing characteristics of bridge pile foundation.The paper,by depending on the actual situation and geological conditions of a railway bridge construction site,takes the approach integrating the vertical static compression test of single pile,theoretical research and numerical analysis to research vertical bearing characteristics of bridge pile foundation,so as to provide certain reference for real bridge engineering.Main work and research results are presented as below:(1)Vertical bearing capacity of single pile is analyzed through the on-site vertical static compression test of single pile at the railway bridge construction field,and the maximum vertical bearing capacity of single pile is concluded according to the load-settlement curve obtained from the test.Finite element software is used to analyze the vertical bearing capacity of single pile and the conclusion is compared with the test result.The study shows that the error of single pile ultimate bearing capacity existing between finite element simulation value and test value is within a reasonable range,verifying the rationality of finite element model as illustrated in the paper.(2)The vertical bearing characteristics of pile group foundation are studied through building finite element model of the bridge pile group in the actual bridge engineering.The paper discusses the differences of the settlement values of corner pile,side pile and center pile at pile group foundation under the equal load.The research shows the settlement value of center pile is the deepest,with that of side pile second deepest and corner pile sees the smallest settlement.The vertical ultimate bearing capacity of pile group foundation in the actual bridge engineering,as studied by using finite element approach,is compared with theoretical calculation value.And the result shows reasonable error between two values,which proves that it is feasible to take the load corresponding to the settlement value of center pile reaching 0.05 times of pile diameter as the ultimate bearing capacity of pile group foundation.(3)Finite element models are built for multiple working conditions with changing pile diameter,pile length and pile spacing.The impacts of changing pile diameter,pile length and pile spacing on the vertical bearing characteristics of pile group foundation is explored by the load-settlement curves of pile group foundation under various working conditions.The study shows that in the process of vertical load increasing,larger pile diameter,longer pile length,or bigger pile spacing helps raise the vertical ultimate bearing capacity of pile group foundationand reduce the settlement of pile group under same load.However,after the pile diameter or pile length increases to a certain level,the effect of larger pile diameter or longer pile length on improving the vertical ultimate bearing capacity and reducing the pile group settlement becomes inconspicuous.(4)The impact of different pile spacing on pile group effect is studied by adopting the approach of fitting pile group effect coefficient curve,and the function curves and expressions between the ratio of pile spacing and pile diameter and the pile group effect coefficient are established.The study shows,for the bridge pile group foundation under the geological conditions of the actual bridge engineering,when pile spacing is equal to or bigger than 8 times of pile diameter,the impact of pile group effect could be ignored.The pile group effect coefficient as calculated by this function expression is helpful for optimizing the empirical value of pile group effect coefficient usually adopted during construction.It can be used to calculate the vertical ultimate bearing capacity of pile group foundation of bridge whose geological conditions are similar to those of the actual bridge engineering.