Introduction
Pile Integrity Test (PIT), or “low strain impact integrity testing of deep foundation” is a widely used
non-destructive test method for the evaluation of pile quality, and integrity. The test can also be used
to estimate the unknown length of existing piles and foundations. In the low strain impact integrity
testing, the response of the pile to an impact on the head of the pile shaft is determined by a high
precision transducer mounted on the pile head. The transducer can either be an accelerator, or a velocity
sensor.
Methodology
- A small metal/hard rubber hammer is used to produce a light tap on top of the pile. The shock
traveling down the length of the pile is reflected back from the toe of the pile and recorded through a
suitable transducer/accelerometer ( also held on top of the pile close to the point of impact ) in a
computer disk or diskette for subsequent analysis.
- The primary shock wave which travels down the length of the shaft is reflected from the toe by the
change in density between the concrete and sub-strata.
- However, if the pile has any imperfections or discontinuities within its length these will set up
secondary reflections which will be added to the return signal (see Fig. 1 ). By a careful analysis of
the captured signal and a knowledge of the conditions of the ground, age of concrete, etc, a picture of
the locations of such problems can be built up.
- The reflected stress wave can be monitored using either processing technique, the observed signals are
amplified and converted into digital display as velocity versus length or frequency versus mobility
records, providing information on structural integrity of piles. The stress wave velocity and
approximate pile lengths are provided as input for the integrity testing.
Result
The low strain pile integrity test results can be used to study the following:
- Changes in the Pile Cross Section
- Discontinuity in Piles (Voids, major cracks)
- Consistency of Pile Materials (Concrete quality, segregation, honeycombing, soil inclusion)
- Estimate Pile Depth
