Geophysical Subsurface Characterization to Estimate Top-of-rock Elevation for Deep Foundations in Challenging Geologic Settings: Numerical Investigation of Full Waveform TomographyÂ-Video

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Joseph Koh presents a numerical study evaluating geophysical methods for estimating bedrock depth in sites with highly variable geology, where conventional borings provide limited information between measurement points. The researchers compared seismic refraction, multichannel analysis of surface waves (MASW), and full waveform inversion (FWI) using a synthetic model of variable weathered-rock thickness.<br /><br />Seismic refraction substantially overestimated rock stiffness and placed competent bedrock too near the surface. MASW produced overly soft, smoothed results and failed to identify competent rock. FWI tracked the bedrock topography more accurately, generally coming within a few meters, but sometimes misestimated depth by five or six meters and overpredicted the thickness of the weathered zone.<br /><br />More reliable bedrock estimates could improve deep-foundation design and reduce construction surprises. However, FWI requires intensive computation and high-performance computing.

Keywords

bedrock depth

geophysical methods

seismic refraction

MASW

full waveform inversion

deep-foundation design