Study On Mechanical Properties And Bearing Characteristics Of Miniature Steel Pipe Piles For Medium And Small Span Bridge Foundations

Miniature steel pipe piles are widely used in engineering due to their excellent engineering characteristics.For small and medium-span bridges,which are accompanied by a small construction area and are located in densely populated areas,they require no major disturbance to the surrounding environment.The advantages of the pipe pile foundation are obvious.In order to deeply understand the mechanical characteristics of micro steel pipe cast-in-place piles,this subject conducts research on the mechanical properties of grouting micro steel pipe piles and the mechanical performance of micro steel pipe piles used in small and medium-span bridge foundations.It is instructive to the construction and design of micro steel pipe piles.In this paper,first,through laboratory axial pressure tests and numerical simulation comparison verification,comprehensive analysis of the ratio of steel pipe diameter to pile diameter under axial static load(d/D),steel pipe wall thickness t,pile length H,grouting strength,etc.The influence of these factors on the bearing and deformation characteristics of piles.The results show that as the diameter ratio d/D of the steel pipe to the pile increases,the ultimate bearing capacity of the micro steel pipe pile increases correspondingly,and d/D of 0.4 and 0.72 are the critical values for the significant change in the ultimate bearing capacity of the pile.Pile failure is mainly caused by three kinds of failure modes: steel tube buckling failure,joint failure of steel tube and outer slurry,and steel tube outer slurry failure.The formulas for calculating ultimate bearing capacity of micro steel tube piles under different failure models are given.The ultimate load value of the pile increases linearly,while the axial load and axial strain curve of the pile gradually develops from the softening characteristics when the wall thickness is small to the ideal plasticity and hardening characteristics;as the pile length increases,the ultimate bearing capacity of the pile first appears very slowly decreasing trend,when H/D> 4,the ultimate bearing capacity of micro steel pipe piles decreased significantly;the increase of grout compressive strength under the same pile diameter had no obvious effect on the bearing capacity of micro steel pipe piles.Further,using the previous research results and combining typical geological conditions in Chengde as the engineering background,the pile performance of the micro steel pipe pile under vertical and horizontal loads is simulated based on the displacement loading method,and the single pile length L,Factors such as diameter D,group pile spacing S,pile arrangement,and number N of piles affect the mechanical properties of single and group piles.The research results show that the reasonable range of pile length design is between 10-15 m,and the increase of the single pile diameter increases the horizontal bearing capacity of the pile;The distance between piles is S=5D,which is the critical distance value where the ultimate load value becomes stable;The pile spacing is between(4-6)D,the group pile effect coefficient approaches 1and the average single pile bearing capacity in the group pile has the largest effect;the average single pile limit of the plum blossom arrangement is relative to the rectangular arrangement;The bearing capacity increases obviously,and the group pile effect is lower;as the number of piles increases,the bearing capacity gradually increases,the ultimate load increases approximately linearly,and the group pile effect becomes more obvious.