Research On Vertical Bearing Characteristics Of Pile Foundation With Sediment Defects

With the rapid development of China’s economy,the construction of large-scale bridge projects has developed rapidly,and pile foundations have been widely used.Group pile foundation is a main form of bridge pile foundation,and its bearing and deformation characteristics have been the focus of research.According to incomplete statistics,millions of pile foundations are constructed each year,but at the same time,due to the impact of construction quality,the overall qualification rate of pile foundations barely reaches about80%,and the proportion of pile foundations with different degrees of defects,especially sediment defects Larger.If the defective pile is not handled properly,it will seriously affect the performance of the superstructure and cause great safety hazards,endangering the safety of life and property.At present,the theoretical research on pile foundations with slag defects is relatively inadequate.Most of them use the methods of early experience,elastic theory analysis,indoor model tests and numerical simplified analysis to conduct research on pile foundation settlement deformation and bearing capacity.In particular,the effect of the existence of defective piles on the bearing characteristics of the group pile foundation and the influence on the superstructure is less involved in the existing research results.In this paper,the theoretical analysis of the vertical bearing characteristics of pile foundations with slag defects is carried out,and the engineering research combined with numerical simulations are carried out.This provides an important reference for further analysis of the bearing characteristics of pile groups with slag defects.First,based on the analysis of the load transfer mechanism of the pile-soil system,based on the load transfer function of the elastoplasticity of the soil on the side of the pile and the weakening of the tri-fold line of the soil at the end of the pile,the load transfer of the bored pile foundation with slag defects under different conditions was established.The theoretical model and corresponding calculation formulas,and the accuracy and reliability of load transfer have been verified,and both are suitable for indoor and field tests.Secondly,the influence coefficient of pile foundation slag defect is defined,the calculation formula of the influence coefficient of single pile and group pile foundation slag defect is derived,and the parameter analysis is carried out.An evaluation index of the bearing characteristics of the pile foundation is obtained.With the increase of the pile diameter,the defect coefficient of the single pile gradually decreases and tends to ease,gradually increases with the increase of the pile length,and increases with the increase of the sediment thickness.Gradually reduced and verified the requirement of the thickness of the friction pile sediment in the "Technical Specifications for Building Pile Foundations"(JGJ94-2008)is not more than100 mm.Finally,the ABAQUS finite element software was used to carry out numerical simulation analysis of the bearing characteristics of the pile foundation with slag defects,and the results were compared with the theoretically derived calculation results.The order of sensitivity of the bearing capacity of the single pile with slag defects to the material parameters was obtained.It is: thickness> elastic modulus> cohesive force> internal friction angle;combined with the influence factor of slag-containing defect on the bearing capacity of pile group with slag-containing defect,the analysis shows that the greater the defect influence coefficient,the ultimate bearing capacity of the pile foundation The smaller the force loss value is,the better the bearing performance is.The degree of influence of the pile foundation position with slag defects on the bearing capacity: angle pile> side pile> medium pile.The effect coefficient of group pile defects gradually decreases with the increase of the number of defective piles.Its load-bearing capacity has a gradual downward trend;under the same load after entering the plastic phase,the area at the top of the cap is increasing gradually with the increase of the number of defective pile foundations,resulting in uneven settlement.