Effect of Pile Geometry on the Interpretation of Pile Integrity Test Results by Numerical Simulation

The most important point in performing the Pile Integrity Test (PIT) is the correct interpretation of the results. This insitu tests is very useful in the estimation of the pile length embedded in the soil or the control of the cross section of bored piled where the quility of the pile construction is in doubt. Two common defects of the bored piles are buldging and necking of the pile cross section which correspond to the over-size and narrowing of the pile diameter alonng the pile length. Thses two anolamies in the pile geometry inflence the pile functionality and an approperiate reaction is required. Correct identifications of the length and dpeth of an anomaly are among the factors that are influenced by the anomaly location and the interaction of the waves passing through the pile. In this research, an attempt is made to interpret the results of PIT by examining the dimensions and location of anomalies in different parts of the pile as well as the effect of the presence of soil on the obtained results. PIT is simulated by the numerical finite difference method and the results have been investigated. The pile head is loaded by a semi-sinusoidal impact which is defined as a compressive pressure over a circular region at the cross section centroid during a short period of time. The verification of the simulations is established by the compariosn of the results with those one-dimentional wave theory which is based on the arrival time of the impact wave to the reciever situated on the pile head. In addition, by changing the position of the wave vreciving in the numenrical mode, it was shown that the best place to install the accelerometer as the recivier would be at the distance of 0.6R from the pile center where R is the pile radius. This finding is consistent with the results of previous studies which confirms the validiy of the simulations. According to the results, the existance of the soil around the pile causes to deform the figure of the waves and it required to modify the records before a correct interpretation. The soil atound the pile plays a role of damper of the waves passing through the pile and it causes that the magnitude of the peaks observed in the records diminish and the interpretaion may not be so easy as that in a free pile. For the pile embeded in the soil, the closer the anomaly location is to the pile head, the less the damping effect of the soil is and thus, the wave forms are more similar to the free pile. Based on the findings of this study, to interprete correctly the PIT results, it is recommended to use the first peak of the recorded velocity if there is a necking defect, while the use of the second peak is recommneded for a buldging defect to estimate the anomaly depth based on the free pile diagrams.It is also seen that as the defect length increases to about twice the diameter of the pile, the peak value of the velocity changes (in most cases, it increases) and remains almost constant at larger lengths.