Study On Vertical Bearing Characteristics Of Pile Group Foundation Of Highway Bridge

At present,there are a lot of researches on the bearing characteristics of single pile at home and abroad,but the bearing characteristics of pile group under vertical load are obviously different from that of single pile,and there is pile group effect within a certain range of pile spacing.At present,although there are different means and methods for the study of pile group effect,the principle of stress superposition or the concept of mutual influence coefficient is mainly used to study the overall bearing characteristics of pile group.In addition,there are few systematic studies on the vertical bearing characteristics,pile group effect coefficient and vertical bearing capacity calculation formula of high and low cap pile groups of highway bridges under the influence of different pile length,pile diameter and pile spacing.Therefore,in this paper,centrifugal model test,numerical simulation,theoretical analysis and other means will be used to systematically study the vertical bearing characteristics and pile group effect coefficient of highway bridge pile group foundation under the influence of different pile length,pile diameter and pile spacing,and on this basis,a more reasonable calculation formula of vertical bearing capacity will be put forward.In this paper,the centrifugal model test is used to explore the difference of bearing characteristics between pile group and single pile.Secondly,the numerical simulation is used to analyze the change rule of bearing characteristics of pile group foundation of highway bridge under different pile length,pile diameter and pile spacing.Finally,a more reasonable calculation formula of vertical bearing capacity is deduced through theoretical analysis.The main results are as follows:(1)Under the same level of vertical load,the end resistance of a single pile in a pile group is significantly less than that of a single pile,but there is a certain end resistance enhancement effect in a pile group,which makes the end resistance of a single pile only about three times of that of a single pile in a pile group.(2)When the load level is small,the pile side friction strength increases gradually along the pile body depth.When the load level is large,the pile side friction strength decreases first and then increases along the pile body depth.A section of negative friction will appear in the upper part of the pile body near the pile cap,and the area of negative friction is within 2m from the bottom of the pile cap.At about 1/3 distance from the bottom of pile group,the friction strength of pile side will increase obviously.(3)The pile group effect coefficient of high cap pile group foundation is larger than that of low cap pile group foundation,but the trend of the two is basically the same.When the pile length increases,the pile group effect coefficient decreases gradually.When the pile diameter increases,the pile group effect coefficient decreases linearly,but the change range is small,not more than 6%.When the pile spacing increases,the pile group effect coefficient increases linearly.