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.