Detection of Voids in Karstic Terrains with 3D Surface-Based Seismic Waveform Tomography

Identification of voids in bedrock is important for the design of deep foundations. Driven piles are often socketed near the top of bedrock due to driving refusal, thus it is crucial to image voids below the pile tips for the reliability of foundations. One of the effective ways for void imaging is the seismic waveform tomography. For demonstration, a 3D full-waveform inversion (3D FWI) method is utilized for detection of buried voids at two test sites in Florida, USA. For the experiments, a 2D grid of geophones were deployed on the ground surface to measure seismic waves induced by active sources. The measured data is then inverted to obtain 3D S-wave velocity profiles. The experimental results reveal that the 3D FWI method can characterize voids at various depths (5–30 m) and variable soil/rock slayers. The existence and location of voids are confirmed by invasive tests.