FEM Model Analysis Of Explosion-expanded Group Pile Foundation Under Lateral And Pull-out Loads

With the development of construction in commercial and industrial area,various forms of piles have been widely used.In this paper,based on the application of the pile explosion-expansion device patent,a new type of expanded pile-exploding steel pile is proposed.The explosion-expanded steel pipe pile is the basic configuration of the steel pipe as a pile,and the explosion expansion device is used to expand and form the explosion expansion ball at a certain point along pile height on the construction site.Different from conventional piles with enlarged bottom,explosion-expanded steel piles have many advantages such as short construction period and high economic benefit,especially for the improvement of the level of the pile foundation on pull-out capacity.At present,the research on the stability and technical characteristics of the explosion-expansion composite pile foundation and its theoretical analysis are still in the preliminary stage.Therefore,it is of great scientific significance and engineering practical value to carry out in-depth and specific theoretical analysis and numerical calculation for the deformation mechanism and strength characteristics of the explosion-expanded Group pile foundation under different loads.In this paper,a finite element software ABAQUS is used to perform three-dimensional nonlinear numerical analysis,displacement control methods are used to simulate the failure mechanism and load characteristics of the explosion-expanded composite pile foundation in loess foundation under different loading modes.Research indicates:(1)There are two load transfer paths for explosion-expanded Group piles under vertical pull-out loads.One is the frictional force in the pile-soil contact interface,and the other is the pile-soil normal stress at the explosion-expanding ball area.The QS curve of the pile foundation has no obvious inflection point.(2)The Q-S curve of the Group pile foundation under the horizontal load has no obvious inflection point.When the horizontal displacement of the pile foundation reaches a certain limit value,the Group pile foundation is considered to be failed.(3)The maximum axial force distribution of each pile under the vertical upward pulling load is happened at the top of the pile and gradually decreases with the increase of depth.The axial force of the Group pile foundation with explosive dilatation ball will exist at the position of the explosion expansion ball.One obvious mutation,especially in the lower part of the explosive expansion ball,is a large amount of mutations.(4)The strength of pile foundation with different piles varies greatly under the action of uplift load.The increase of the blast expansion ball at the bottom of the pile will increase the ultimate pulling up capacity of the Group pile foundation.With the double-ball pile foundation,it can be seen that increasing the blast expansion ball on the upper part of the pile has little effect on the lifting capacity of the pile foundation.Theoretically,the more the blast expansion ball,the higher the pull-out resistance capacity of the pile foundation.(5)Under the horizontal load,the addition of a burst expansion ball to the lower part of the pile body improves the horizontal pulling up capacity of the pile foundation.However,the addition of the blast expansion ball to the upper part contributes very little to the horizontal pulling up capacity of the pile foundation.The increase of the pile diameter is the most obvious improvement of the horizontal pulling up capacity of the Group pile foundation.(6)Under different pile spacing conditions,the resistance capacity of Group pile foundations of various types of piles under vertical pull-out load is very close,and the slight increase in pulling up capacity is mainly due to the increase in the self-weight of pile foundation platform and the change in pile spacing.The improvement of the horizontal resistance capacity of each pile type Group pile foundation is obvious.