Full Waveform Tomography of Parallel Seismic Data for Evaluation of Unknown Foundations: Fid-Bau Portal

Full Waveform Tomography of Parallel Seismic Data for Evaluation of Unknown Foundations

Kordjazi, Alireza / Mahvelati, Siavash / Coe, Joseph T. / Alidoust, Pourya

The evaluation of unknown foundations continues to be an important issue with the increasing interest in foundation reuse and rehabilitation. Several nondestructive testing (NDT) and geophysical methods have been proposed to characterize unknown foundations. One of the most robust methods is the Parallel Seismic (PS) method, which was purposely developed to determine the unknown or undocumented depth of foundations. The PS method relies on recording the arrival time of waves at a borehole alongside the foundation after the top of the foundation is struck by a hammer. When the arrival times are plotted as a function of depth, the foundation bottom can be located at the break in the slope of the arrival times. This break in the slope occurs once the downward propagating wave moves pass through the foundation into the soil surrounding the toe of the foundation. Several studies have shown the robust capabilities of PS on both metallic and non-metallic foundations. However, there are a number of issues present in the PS method, including complications introduced by foundation flaws. To address this concern, this paper presents the use of full waveform tomography with PS data on a synthetic soil-foundation model. Rather than rely solely on first arrival times, the full waveform tomographic approach attempts to solve an inversion problem that matches the entirety of the measured PS waveforms with waveforms acquired from numerical simulations of wave propagation in a subsurface model. The results of this study demonstrate that the full waveform PS approach provides a more comprehensive evaluation of the unknown foundation geometry, particularly the extent of anomalous conditions.