Analysis Of Pile Foundation Mechanics Characteristic Of Large Diameter Medium Pile Excavation Station With Single-layer Guide Hole

Based on the self-balancing test of large diameter middle pile in single-layer pilot tunnel of Beijing Metro Line 16,the test data are compared and analyzed.The finite element method is used to simulate the self-balancing test of pile foundation,and the factors influencing the bearing capacity of pile foundation are analyzed.Comparing and analyzing the mechanical characteristics of pile foundation under top loading and self-balancing loading,the conclusions are as follows.:(1)Statistical analysis of load-displacement curve of pile foundation by self-balancing method shows that the bearing capacity of pile foundation in pebble layer is much larger than that of pile foundation in silty clay layer.Large plastic deformation and small elastic deformation occur in the soil at the bottom of the pile.Increasing the length and depth of pile significantly increases the bearing capacity of pile foundation.(2)The finite element method is used to simulate the self-balancing test of pile foundation at Wanquanhe Bridge Station of Beijing Metro Line 16.The simulation results prove that the FEM analysis of the self-balancing test of pile foundation is reasonable.The simulation results prove that it is reasonable to analyze the static load test of pile foundation by finite element method.(3)The influence factors of bearing capacity of large diameter pile foundation are analyzed by finite element method.The results show that the bearing capacity of pile foundation can be improved by increasing the compressive modulus of soil,and the cohesion of soil has no obvious influence on the bearing capacity of pile foundation.Increasing the length,diameter and depth of the pile can improve the bearing capacity of the pile foundation,and the diameter and strength of the pile have no obvious influence on the bearing capacity of the pile foundation.Increasing the stiffness of pile-soil interface can improve the bearing capacity of pile foundation,and the cohesion,expansion angle and friction angle of interface have little influence on the bearing capacity of pile foundation.(4)Comparing and analyzing the self-balancing method and the traditional static load pile-pressing test,the research shows that the compressed pile produces smaller compressive deformation.Upward displacement occurs on the side soil of the upper pile.Suggested values of revised coefficient of bearing capacity of pile foundation and new equivalent transformation method are proposed.In gravel and sandy soil layers,the depth of pile foundation has no obvious influence on the correction factor of pile bearing capacity,and the location of loading point has a great influence on the correction factor of pile bearing capacity.