Detection of wave velocities, thickness of slab and void location using impact echo in combination with MASW tests

This study aims to detect the compressional (VP) and shear wave (VS) velocities, alongside the thickness (h) of a slab with and without voids, utilizing impact echo (IE) in conjuction with multichannel analysis of surface waves (MASW) test. These non-destructive methods are highly recommended when only the top surface of the slab is accessible. During IE analysis, calculating (h) purely from the predominant frequency (f) and VP is challenging because the beta factor (β) depends on Poisson’s ratio (V). Through experimental testing and finite element axisymmetric simulations, this research proposes an approach allowing IE and MASW testing without assuming (V) or any rigorous inversion analysis to compute (h) and (VS). Results demonstrate that the error in determining thickness by approximating beta instead of using its calculated value is insignificant. Furthermore, up to a 5% deviation in measured frequencies hardly affects the calculated thickness. For accurate IE interpretation, the input excitation frequency must fall within a specific range, and recording both horizontal and vertical acceleration components is recommended. Regarding voids, their location primarily affects the predominant frequency, whereas void size has minimal impact. Finally, ultrasonic pulse velocity (UPV) tests successfully validated the predicted wave velocities from MASW and IE tests.