Existing Bridge Pile Foundation State Evaluation Based On Dynamic Stiffness Test

Static load test and dynamic pile testing method are widely used in the pileintegrity and bearing capacity test and evaluation. but the static load test and highstrain dynamic pile testing method will cause the relative displacement between thepile and the soil, even will cause some damage to the pile, so the static load test andhigh strain dynamic testing method has some difficulty in the detection of existingbridge pile foundation. Low strain dynamic pile testing method can strongly fit for thefield conditions and be easily operated, so it’s suitable for the test and evaluation ofexisting bridge pile foundation.The mechanical impedance method is one of the low strain dynamic pile testingmethods, which has been approved for pile integrity testing. Based on the basicprinciple of transient mechanical impedance dynamic pile testing method, the authortested the foundation piles of an existing bridge by the method after the improvementin equipment of transient excitation. In a certain geological conditions, dynamicstiffness test results have a certain relationship with the integrity of pile, pileproperties, geometric parameters and the excitation force. In the paper, the authoranalyzes the relationship between dynamic stiffness and the parameters of pile-soilsystem, and the relationship between dynamic stiffness and the excitation force.To further verify the test results, but also for the analysis of the influence of piledefects on the dynamic stiffness, using the Midas GTS software, the3-D finiteelement model of pile-soil system was computed and analyzed. By the calculationresults, author analog the dynamic response of defective piles, such as the piles withinternal voids, necking defects, low concrete strength and the broken piles.Finally, author summarize the method based on dynamic stiffness to evaluate thefoundation piles’ integrity and bearing capacity, And propose method to estimate thebearing capacity of existing bridge foundation piles using dynamic stiffness.Based on the test results and simulation results, the paper verify the correlationbetween pile Integrity and dynamic stiffness and provide a basis for estimating theexisting bridge foundation piles’ bearing capacity by dynamic stiffness, which hashigh reference and guidance to the testing and evaluation of the bearing capacity ofpile integrity.