Study On The Numerical Simulation Of Pile Low Strain And Defect Quantitative Analysis

Pile foundation is the most widely used of a base type,especially for high-rise buildings,large areas of industrial buildings,and poor geological conditions,its quality fit and unfit quality directly related to the structure of the use fixed number of year and safety performance.Pile testing key steps for testing its quality,plays an increasingly important responsibility.Q ualitative detection is not enough,therefore,only the quantitative analysis in the evaluation of pile quality levels also plays an important role.At present,the qualitative detection of pile and there are many shortcomings,quantitative analysis also does not have a unified standard.In this paper,the stress wave propagation theory,analysis of stress wave propagation in one-dimensional elastic rods,introducing impedance concept and discussed in different reflection of variable impedance interface,adding stiffness and damping coefficients of the wave equation is established and solved.Complete change of pile,single defect,defect velocity response of pile top is analyzed by ANSYS/LSDYNA finite element program,then analyzes the influence of pile side soil damping,elastic modulus,pulse width,defect depth of stress wave propagation.According to the principle of energy distribution at the interface of variable impedance,the corresponding relation between energy distribution and the degree of defect is obtained,mathematical statistics table L₁₈?6×3⁶?,the influence of damping,elastic modulus,exciting impulse and radius of pile on the attenuation of stress wave is analyzed.It is concluded that damping is the key factor,and the quantitative formula of the defect is established,and the reliability is verified by an example.Research shows that the determination of a pile top position speed response diagram,according to the law and the theory of reflection wave impedance stress,can initially determine the basic types of defects into the reflection wave peak and the corresponding time for defect quantification.The pulse width of exciting force will have some influence on the detection accuracy.When the pulse is too wide,the detection accuracy is low,and the pulse is too narrow,so it is difficult to obtain a clear reflection of the bottom of the pile.The soil damping and elastic modulus of the pile side have little influence on the stress wave velocity.The velocity of the wave in the pile is considered to be the definite value,and the damping has a great influence on the attenuation of the wave amplitude and has little influence on the elastic modulus.By orthogonal test,the damping of soil on the side of pile can significantly affect amplitude attenuation,and the quantitative formula of the defect is established.The reliability of the soil is proved by numerical simulation.