Study On Low-strain Quantitative Analysis Of Pile Defects In Time Domain

At present, it is still very difficult to determine the degree of pile defect quantitatively in engineering practice. In order to establish a new low-stain method to realize quantitative analysis of pile defects considering pile-soil interaction, researches have been done as following.The pile wave equation with damping is developed with one dimension wave theory considering pile-soil interaction. Using the analytic solution of the equation, orthogonal tests were conducted to analysis the effect of different parameters on the attenuation rule of velocity wave along pile shaft. The result showed that the coincident functional relationship between wave amplitude ratios and pile-soil interaction damping coefficient could be determined corresponding to different projects. Then, the relation between the damping coefficient and amplitude ratio of reflected velocity wave to incidenced velocity wave on pile top was established. Then a method to determine damping coefficient of pile-soil interaction was developed based on velocity response of pile top.The transmitting process of velocity wave was analysed based on the attenuation rule of velocity wave along pile shaft and the distribution relations of enegy where wave impedance changed. Corresponding to different numbers of defects and different beds of strata, the relationship for quantitative analysis of pile defects was determined.The pile-soil interaction model tests were proceeded to measure the pile-soil interaction damping coefficient of six different kinds of soils. Then, shear wave velocity experiments were proceeded corresponding to the conditions of pile-soil interaction model tests. With the result, the relationship between the damping coefficient and shear wave velocity was founded. Then, the theoretic damping coefficient were determined with the theoretic formular. Result showed that theoretic damping coefficients should be corrected in engineering practice, and the correction factor was a function of shear wave velocity. Moreover, corresponding to the result of measured damping coefficients, high-stain damping coefficients have a great error. Therefor, it is improper to apply high-stain damping coefficients in low-stain conditions.In order to spread the method of determing damping coefficient with shear wave velocity, model test of integrated pile and shear wave velocity experiments using two kinds of sand were conducted. Results showed that calculated damping coefficients were consistent with test results.The quantitative analysis of pile defects of defective model pile in the homogeneous soil had been done with calculated damping coefficient and the relationship of quantitative analysis of pile defects. The result showed that the calculated degree of pile defects was consistent with the actual result.The velocity signals on pile top were dealed with wavelet analysis method. The decomposing result showed that smallscreen of pile bottom appeared in the the approximation signal.