Numerical Assessment of Factors Affecting Waveform Based on Low Strain Testing of Piles
In this paper dynamic testing of piles using the low strain method is performed by means of numerical analyses based on solid finite element model. To this end, velocity-time curves are presented investigating the influence of various parameters such as mesh density, impulse width, receiving point, and soil modulus on the waveform characteristics. Then, find regularity of waveform affected by different parameters to provide reference of the real project detection.
LOW STRAIN INTEGRITY TESTING OF PILES: THREE-DIMENSIONAL EFFECTS
Results of low strain integrity testing of piles are normally interpreted using one-dimensional (1D) stress wave theory. While 1D stress wave theory is acceptable for pile-driving analysis, it may not adequately simulate the response of piles in sonic integrity tests where the hammer is small in relation to the size of the pile. Extensive parametric studies were performed using 1D and 3D (axisymmetric) wave equation models to study this problem. The main 3D effect in intact piles lies in the initial velocity response that becomes negative after the first positive peak. This response resembles that of a pile with an anomaly near the pile head. If this is not recognized, it will lead to a wrong assessment of the pile condition with attendant cost implications. This potential source of error can be removed by maintaining a distance between hammer and receiver that is greater than 50% of the pile radius.
DYNAMIC RESPONSE OF INTACT PILES TO IMPULSE LOADS
The objective of this work was to evaluate the theoretical capabilities of the non-destructive impact–response method in estimating the length and cross-sectional area of intact piles. Three-dimensional (3-D) axisymmetric finite element models were developed to simulate the testing. The results obtained were compared to one-dimensional solutions to evaluate the importance of 3-D effects. Extensive parametric studies were then performed on piles without defects. In each parametric study, the results from the direct use of time histories of displacements or velocities, the mobility function and the Fourier transform of the recorded displacements (impact-echo method) were compared in order to assess their relative advantages and disadvantages. The effects of the relative stiffness of the surrounding soil to that of the pile and of the embedment depth were also investigated for all three methods. In a companion paper the use of these procedures to detect defects such as bulbs (increases in the cross-sectional area of the pile) or necks (decreases in area) is studied. © 1997 by John Wiley & Sons, Ltd. Int. J. Numer. Anal. Meth. Geomech., vol. 21, 255–275 (1997)