PSI - Issue 62

Stefano Stacul et al. / Procedia Structural Integrity 62 (2024) 185–192 Stefano Stacul and Nunziante Squeglia / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 3. Dual-sensor Impulse-Echo testing scheme

The receiver probe inside the tube is generally a hydrophone while the source of the signal is a hammer with an integral trigger device. The probe is lowered down the bottom of the tube and the hummer blow generates the impulse, then, the signal is recorded by the hydrophone and finally the signal is analyzed to assess the arrival time. These operations are repeated every time the hydrophone is moved upwards (with uniform increments). As the hydrophone depth varies in consistent increments, the travel time will also change proportionally. This is true if the probe is close to the foundation, if the probe is below the base of the foundation the transit time will increase significantly (more than proportionally) due to the lower stiffness of the soil compared to that of the foundation material. Obviously also a defect can be detected for the same reason. Typical test arrangement and results are presented in Figure 4. Alongside the foundation first arrival points draw a line with a uniform slope which is dependent on the wave velocity of the foundation material. Starting from a certain depth the single-slope line described above will inflect, thus denoting the depth of a relevant defect or the foundation base.

Fig. 4. PS test apparatus, arrangement, and typical results (ASTM D8381-21)

In the following Table 1 a list of available Standards and recommendations of the methods discussed above is reported.