Research On Integrity Detection Of Foundation Piles Based On Ultrasonic Transmission Method

With the development of society and economy,there are more and more large projects such as highway,bridge and high-rise building,among which the construction of foundation pile plays an important role in the safety of the project.As a hidden engineering,foundation pile is affected by construction environment,construction technology and other aspects,so it is easy to produce defects,so it is necessary to carry out integrity detection.In this paper,a foundation pile integrity detection system based on ultrasonic transmission method is designed,which provides a detection platform for acquiring foundation pile data,and the integrity of foundation pile is judged by fuzzy comprehensive evaluation method.Firstly,this paper introduces the acoustic principle and testing process of ultrasonic transmission method,and then carries on the design of the hardware and software functions of the foundation pile testing system.The hardware circuit includes a conditioning circuit and a power supply.The conditioning circuit includes excitation,amplification,filtering and voltage lifting functions.The power supply part uses a dual power supply of mains and lithium batteries.The software part includes the lower computer and the upper computer.The lower computer adopts STM32 platform to carry out dual ADC data acquisition for ultrasonic signal,and establishes communication link with the upper computer through serial port to realize data transmission.The upper computer realizes data processing of the ultrasonic signal collected by the lower computer through Qt cross-platform software,which lays the foundation for the automatic online detection of foundation piles in the later stage.Secondly,in the follow-up processing and algorithm of digital signal acquisition,the influence of different sampling points and sampling time intervals on frequency domain characteristics of ultrasonic signal is discussed,and the instability of the main frequency criterion is obtained.Therefore,frequency is not used as the evaluation parameter of the integrity detection of foundation pile.At the same time,the frequency domain filtering method is used to filter the signal high and low frequency noise,and the time domain signal without delay and waveform distortion is obtained.The acoustic parameters are extracted according to the time domain signal and reference to the specification.Fuzzy comprehensive evaluation method was used to establish a three-level pile integrity evaluation system of acoustic measurement line,cross section and pile.Acoustic parameters of sound velocity,wave amplitude and waveform were selected as evaluation indexes.The index weights of acoustic parameters were determined by three-scale analytic hierarchy process,and the corresponding membership functions of each parameter were set by F-distribution method and the abnormal degree determination table of acoustic parameters.Then,the integrity function value of single measuring point is obtained by fuzzy calculation.Finally,the integrity function value of cross section and pile is obtained according to the specification,so as to determine the integrity level of pile.Finally,in order to verify the rationality and feasibility of the fuzzy comprehensive evaluation method for pile integrity grade evaluation,the fuzzy comprehensive evaluation analysis was carried out on the test data of simulated defective piles.Compared with the single factor evaluation method,the fuzzy comprehensive evaluation method has a better evaluation effect on ultrasonic transmission method to judge pile integrity.