Characterization of Concrete Pile Groups with 2-D Seismic Waveform Tomography

Currently, about 28,000 bridges over water in the United States are classified as having missing key foundation information such as number and distribution of piles and pile lengths. The as-built drawings of buried concrete piles or drilled shafts are critical in assessing the hydraulic scour vulnerability of bridges. This paper presents an application of seismic waveform tomography for characterization of shaft groups. The capability of an existing 2-D Gauss–Newton seismic waveform tomography method was investigated on challenging subsurface conditions for groups of drilled shafts with various lengths within each group. The method was applied to field experimental datasets collected at the National Geotechnical Experimental Site (NGES) at College Station, Texas. The site contains two groups of four and five drilled shafts with various lengths from 10.4 to 24.1 m. Seismic wave fields were measured on the ground surface at the edges of the two pile groups, and analyzed by the 2-D waveform tomography method. Seismic results showed that waveform analysis was able to well characterize the pile groups. Individual drilled shafts and soil between them are distinguished, and lengths were also generally predicted.