OPTIMIZATION AND APPLICATION OF INSTANTANEOUS PHASE DIFFERENCE INTENSITY CALCULATION METHOD TO CAVITY DETECTION BENEATH CAST-IN-PLACE PILE

The two-receiver sonar method for cavity detection beneath piles is an effective detection method in the special environment of mud during the construction of bored holes. The Instantaneous Phase Difference Intensity(IPDI)can be applied to extract weak reflection signal from the top and bottom of a cavity,hence discovering the location of the cavity. However,during the process,how the specific valuing method of some critical parameters influence the detecting results remains unknown. The uncertainty may lead to loss in accuracy. The purposes of this paper are to find out(1)how these critical parameters,such as sampling rate,the number of ensemble members and standard deviation,can influence the results of cavity detecting and (2)the suitable way to value these parameters. First of all,we establish a numerical mode for simulating cavity detection. Secondly,we explore the optimization of valuing the critical parameters through lots of tests of simulated numerical signals. At last,we apply the optimization results to the IPDI analysis of a real-field signal to verify its effectiveness. The gray prediction model is applied to deal with the end effect appearing in the IPDI image. The result shows that a sampling rate of 0.5~1MHz,accepting 0.1 as standard deviation and 300~600 as the number of ensemble members can improve the accuracy of cavity's location and size's detecting results. In addition,grey prediction model can help release the end effect of IPDI image. A solution to address signal's zero drift phenomenon is promoted. By subtracting the trend item from the reconstructed signal,the hidden reflection signal from the bottom of the cavity is discovered. The calculated depth of the cavity's bottom is identical to what it demonstrates in borehole logs. Compared with the original detection results,the optimization method is proved effective in elevating the accuracy of two-receiver sonar method for cavity detection.