The Study Of The Impact About The Pile Parameter And Boundary Conditions On The Low Strain Reflected Wave Method

In the Pile Integrity Testing, there is an important unresolved issue which is using Low Strain Method to fix the pile defect, judge the kind and level of the defect. To improve the accuracy of testing the pile integrity with Reflected Wave Method, it is necessary to build an experiment model with numerical analysis to systematically study the impact of pile parameter and geological conditions on the low strain reflection rule. Several aspects are made in this paper.One-dimension wave theory, the interaction of the stress wave, three-dimension effect of the stress wave and the fitting equation of the stress wave impacted by the pile in soil are introduced. Meanwhile the methods judging the stress wave propagation rule with the wave impedance and the defect location with time domain analysis are recommended.Six models of integrate pile, broken pile, expanding, necking, segregation, clod in pile and stone in pile are built. Besides some issues which should be pay more attention before the experiment with Low Strain Method are dedicated. Meanwhile the relationship between the pile in soil and the stress wave attenuation by studying the impact of the pile geological conditions on the reflected wave is proposed. According to amount of experiments, a more accurate method of judging the broken pile location has been got; Some issues have been summarized which should be paid more attention by studying the thickness of the sediment in the bottom of the hole; The relationship between the size of the local expanding and the low strain reflected wave has been got by comparing three kinds of low strain reflected wave curve of the local expanding; The relationship between the size of local necking and Low Strain Reflected Method has been got by comparing the oscillograms of three kinds of local necking, including the method to judge local expanding and necking. The pile oscillograms of three kinds of segregation thickness are reviewed and the rule of the impact about the segregation thickness on the low strain reflected wave is confirmed. The method to detect clod in pile and stone in pile with low strain reflected method is summarized.The limited numerical model of this method based on ANSYS/LS-DYNA dynamic explicit analysis is built. Meanwhile through the comparison of the experimental results with the models such as broken pile, expanding, necking, segregation, the conditions around the pile, a new method which combines with field test and numerical simulation, also including the exact experimental material parameter and the parameter of the geological conditions around the pile has been got. This method reversely judges the defect kind and location, as well as the defect level.