pile foundations;  ultrasound;  sampling distribution;  Fuzzy comprehensive judgment

Pile foundation is widely used in engineering due to its advantages of high bearing capacity and good seismic performance, but at the same time, as a hidden project, the construction quality of pile foundation is difficult to control well, and engineering accidents caused by poor quality of pile foundation occur from time to time. Therefore, improving the level of pile foundation detection and analysis and identifying the defects in the pile is the premise of engineering safety and durability. In the existing ultrasonic pile analysis methods, the influence of different degrees of defects on ultrasonic sound velocity, frequency and amplitude has not been fully considered, and the corresponding methods for judging defects are relatively general. In view of this, the confidence intervals of the expectation and variance of ultrasonic sound velocity, frequency and amplitude are obtained by using the sampling distribution theorem, and on this basis, the membership functions of "good", "-general" and "poor" of ultrasonic quantity are given, and the ultrasonic detection pile is tested by the method of fuzzy comprehensive evaluation