Defect Pile Detection System

It is necessary to use deep pile foundation for multistory buildings,bridges, marine structures and other special building structures. Even for common building structures, they also need pile foundation to improve their stability, when the foundation state is poor. The quality of pile foundation tell upon the safety of building structures. So it is important to detect the pile's quality with effective means to avoid engineering accident.At present, the reflecting wave method on low strain occupy the most marketplace in detecting the pile's integrality by advantage of its simple and convenient measuring way. But when the pile's section changes gradually, there is no reflection waves in the pile. In this circumstance, the reflecting wave method is no longer applicable. To find a new way to make up this shortage is in urgent need.The paper take the advantage of modal analysis technic in vibration engineering to study the vibration characteristic of the pile system from the vibration theory view. Considering the principle of the mechanical admittance method in pile dynamic testing is to identify the pile's dynamic characteristic through measuring the excitation function and the response function at the head of it. The frequency response function and the impulse response function of the system with single degree of freedom are given first in the paper. So far as the multiple degree of freedom system, is uncoupled in modal coordinate system and then converted to physical coordinate system. Thus the frequency and impulse response function of it can be easily obtained. The pile systems are simplified as different vibration systems with different degree of freedom in the paper. The lumped mass model of the pile system is given. The mechanical admittance spectrums of the intact pile and all kinds of defective piles are computed largely to find out that the mechanical admittance spectrum's characteristic have some coincidence relations with the style and position of the defective piles. So we can detect the quality of the pile foundation according to this characteristic. The paper apply this principle to actual engineering and handle the actual data with proper data processing and spectrum analysis methods. Corresponding processing software is also compiled along with them. The result of actual measurement proves that the method is viable to a certain degree if the model is selected expediently. And the interpretation software has some useful value too.