Analysis On Dynamic Response Of 3D-Defective Piles Using Low Strain Torsional Wave Method

As a kind of deep foundation with large bearing capacity, high strength and wide application range, the pile foundation is widely used in civil engineering. However, due to the factors such as the construction level and the environmental impact of the pile, the pile often appears all kinds of quality problems, which endanger the safety of the building and personal property. Therefore, how to quickly and efficiently determine the type of pile diseases, the degree of disease has become a pile foundation quality inspection project is more and more important research topic.At present, the application of low strain longitudinal wave method in pile integrity testing is the most widely used method. But the longitudinal wave velocity due to the velocity faster, for detection of short, small defects can not effectively. At the same time by the three-dimensional effect greatly, and due to the upper structure interference is larger, the existing structure detection susceptible to bending wave effect etc., in practical applications have limitations. The unique advantages of the torsional shear wave make up the deficiency of the longitudinal wave. In this paper, based on the basic theory of reflection wave method and the method of numerical simulation and model test, the response characteristics of the torsional shear wave. The main work and conclusions of this paper are as follows:(1)Using model test of typical disease pile respectively using longitudinal and torsional shear wave method in the detection of pile foundation in the free state and effect of soil around pile dynamic testing response curve, analyzed the torsional shear wave for typical disease especially short defects, local defect pile the waveform characteristics, summed up the torsional shear wave longitudinal wave with respect to the advantages and disadvantages.(2) Using the ANSYS/LS-DYNA finite element software to simulate the dynamic response curves of the typical diseases of the longitudinal and torsional shear waves and compare with the model tests, the similarities and differences between them are analyzed.Two different impedance algorithms are used to simulate the axial size, defect pattern, defect distribution, longitudinal position of the defect, and the response curve of the pile under the action of the pile. Summed up the similarities and differences of the two algorithms, and put forward the defect axial length affects the critical value expressions, summed up the ring defect central angle, radial dimension, fan-shaped radial dimensions of defect, defect level discrete degree, planar defects distribution area, longitudinal position of defect and pile surrounding soil under the action of pile dynamic measured response rules.(3) Simulation and analysis of the dynamic response curves of longitudinal and torsional shear waves in the pile foundation of the existing high pile bridge. By analyzing the similarities and differences of different excitation receiving methods, a reasonable method of receiving the pier column, pile cap, and the upper structure is proposed.