| Because of its high strength, great loading-carrying capacity and fine durability, pilefoundations have been widely used in civil engineering. However, because the technology ofconstruction was complicated and the level of construction was low, piles often have variousquality problems. And this poses a threat to people’s properties and lives. Therefore, how todetect the the quality problems of piles efficiently and accurately is an important researchtopic in pile foundations.The reflected wave method of low-strain is widely used in pile integrity testing. Bymeans of theoretical and experimental study, combining numerical simulation method, in thisthesis, the response of three-dimensional defective piles to impulse force was researched. Themain research and results involved in the dissertation includes the following parts.Basing on the one-dimensional stress wave theory and combining the model piles’ testingresults, qualitative analysis of the character of low-strain dynamic response of piles was made.Considering the reasonable matching problem of pile and hammer, and combining the resultsof field tests, then, the parameters of hammer’s geometry and material model were determined.The hammer-pile-soil system model was established, and the layering of soil was considered.Through the integrity of pile obtained by the numerical calculation results and experimentalresults verified the reliability of the finite element model for the simulation analysis. This laidthe foundation for the defective pile simulation. Furthermore, the influence of the differentmeasured points on the pile top on dynamic response was researched, and the results showedthat, the influence of the locations of the specification measured point on the amplitude of thereflected wave can be neglected.The character of dynamic responses of defective piles with same coefficient of the pileintegrity but different axial sizes of the pile defect were analyzed. And the expression ofcritical axial value which had an influence on the amplitude of the reflected wave was given.The results showed that, the critical axial value was associated with the properties of thehammer and the duration of the pulse force.The dynamic responses of the axisymmetric defective piles with different coefficients ofthe pile integrity were compared. And the results showed that, as the coefficient of the pile integrity increased, the influence of axial sizes of the pile defect on the amplitude of thereflected wave was greater. Also, the dynamic responses of the three-dimensional defectivepiles with same coefficients of the pile integrity but different defect shape were compared.And the results showed that, as the central angle of the piles defects increased, the influenceof the axial sizes of the pile defect on the amplitude of the reflected wave was greater.The dynamic responses of defective piles which have same coefficient of the pileintegrity, but have different shape and different morphological distribution were researchedseparately. And the results showed that, the influence of the shape and the morphologicaldistribution of pile defect on the amplitude of the reflected wave can be neglected.The comprehensive influence of soils and the defect formations on the dynamic responsesof piles was analyzed systematically. The results showed that, the influences of the soils onthe dynamic response of piles with different defect formations were different. And for specificperformance, as the central angle of the piles defects increased, the influence of the soilmodulus on the amplitude of the reflected wave was greater. And for different shapes of piledefects, the influence of the soil damping on the dynamic response was different. |
