Numerical Analysis Of Passive Pile In Excavation

Piles are generally placed prior to excavation in the foundation construction of a building, which is erected on soft clay subgrade.After excavation,a pile often deflects because of the effect of the horizontal soil pressures,which originate from the horizontal movement of soft clay. In this case,the pile is called "passive pile".When the deflection of the pile is not negligible,it is called "passive defect pile".The formation and development of this type of pile are related to time,so analysis based on linear elastic constitutive model of soil is not exact.Furthermore the bearing capacity of the pile and remedy for it are problems desiderate solving.According to the existing research,analysis for internal force and bearing capacity of "passive defect pile" should be carried out in the formation stage and working stage of it.Finite element method based on pile-soil interaction is combined with viscoelastic constitutive model of soil to simulate the performance of a pile in two stages.The reliability of numerical method is evaluated by contrasting the measured data with that obtained from numerical calculation. Finally,the influences of some parameters to the pile are analyzed and remedy for it is put forward.The outcomes based on the study of "passive defect pile" are as follows:(1) Formulas for calculation of internal force and bearing capacity of the pile in two stages.(2) The characteristic of performance of the pile simulated by numerical method which based on pile-soil interaction and ultimate bearing capacity of it.(3) Evaluation for reliability of numerical method and the influences of some parameters to the pile.(4) Remedy for the case of"passive defect pile".The study indicates that in the analysis of "passive defect pile",time is an important factor that should be in consideration,and the viscoelastic constitutive model of soil is reasonable and effective.The performance of pile in two stages could be simulated by numerical method,which based on pile-soil interaction and viscoelastic characteristic of soil.The pile will bend and the internal force will increase in formation stage because of the horizontal soil movement.When the internal force is large,the piles may be destroyed.The results also show that the internal force of the pile will increase more obviously and it will be destroyed easier in working stage than in formation stage.The ultimate bearing capacity of the bent piles is less than that of a straight pile.Finally,the effects of"passive defect pile" to a project could not be weakened only by improving the quality of pile.Ground improvement could solve the problems caused by "passive defect pile" effectively.