Numerical Simulation On Low Strain Of Foundation Pile And Quantitative Analysis

Pile foundation of railway bridge is an important part of railway project，it is importantto ensure the quality of pile foundation for the security of railway operators.Low strainreflection wave method is one of the methods used most widely now of detecting pilefoundation. It is the difficult point to determine and identify the pile defects at pile testingwork. To one-dimensiong wave equation as foundation，combining with FEA software，thispaper makes systematic analysis and study of problems existed in practical technique of lowstrain reflection wave method. The paper mainly from the following aspects carries outresearch and study:(1) It is proved to be reasonable by program and effective to use dynamic analysisprogram ANSYS/LS-DYNA to build pile-soil model.As to complete pile, it makes researcheson variation features of low strain reflected wave curve under the situation of exciting forcepulse width, pile diameter, low strain reflected wave curve of pile length, different receivingpoints, the changing pile elastic modulus parameter changes variation. And on defectivepiles，it makes researches on variation features of low strain reflected wave curve under thesituation of defect depth, serious level defect length, gradient-section, segregation, fractureand other factors change.(2) In the practical detection process, What’s more Two-velocity method can reduce theimpact of the upper secondary interference structure effectively. This paper, through theestablishment of a complete pile finite element model to use dynamic analysis programANSYS/LS-DYNA.considering the prerequisite of pile damping premise, studies the speedtime curve under the situation of different excitation point, different receiving point, then usesthe program compiled by matlab after extracting data to separate up and down waves, whichreflect the bottom of the pile.to prove that the use of Two-velocity method for pile integritytesting is feasible.(3) Due to the difficulty problem of defects quantitative analysis in the pile testing work,this paper quotes a program to carry on a lot of forward calculation. The program startingfrom the wave equation of the pile-soil system,combining with boundary and initialconditions，constitutes the definite solution of the problem of pile-soil system under transientexcitation,and using difference method，solves the solution of this problem to solve the speedresponse to complete pile as well as a variety of non-complete pile.It also obtaines differentpile side damping coefficient pointing at different soil, the defect levels in different defectlocation and relationship between the incident and reflected wave amplitude in speed time history curve.Through the model pile test,the result shows that the defect quantitative analysisformula proposed is valid and reliable.