The Discussion Of Reflected Singal At The Bottom Of Pile By The Method Of Low Strain Reflected Wave

Due to its lightweight, fast, cheap, easy to prepare, easy to operate and etc, low strain reflected wave method occupies the mainstream position in the pile testing. It has become the most successful pile integrity detection method and the most widely used in China. In the low strain reflected wave method, obtaining the reflected signals of the pile bottom or not is an important criterion to judge the quality of the pile. However, in the actual testing process, the reflected signals of the pile bottom are often undetectable, so it severely affected the accuracy of detection. Therefore, knowing the factors that affect the reflected signals of the pile bottom and solving the problem that cannot detect the the reflected signals of the pile bottom have important practical significance for the the domestic low strain reflected wave method detected industry. This thesis discusses the factors that affect the reflected signals of the pile bottom and its impact law. The main contents are as follows:First of all, this thesis describes the research status of the reflected signal at the bottom of the pile in the low strain reflected wave method, the basic principles of low strain reflected wave method and several factors that cause stress wave energy attenuation. This thesis also briefly describes the reflected wave method detection system, the detection step and test equipment, and recommendations that could help improve the the reflected signal quality and accurate identification of the reflected signal.Secondly, based on the25,000measured data through the low strain reflected wave method, statistical sampling4859measured data of two large-span bridges. In the case of different pile length, pile diameter, testing instruments and geological conditions, the actual situation of the reflected signal at the bottom of the pile in the measured data and the law of the factors and their weights are researched.Finally, this thesis numerical simulates the changes of incident volatility, reflected amplitude, the incident time and reflection time in the case of the different impact energy, pulse width, the location of the measurement points, soil elastic modulus, Poisson’s ratio, severe angle of internal friction, cohesion, pile length, pile diametershaft strength by the finite element program MIDAS/GTS. The influence rules of these factors on stress wave attenuation, delays of incident time and reflected time are investigated. The influence rules of the factors on the apparent extent of the reflected signal at the bottom of the pile are investigated by the ratio of reflection wave amplitude and the incident wave amplitude.