S.R. 0075 Bridge over the Norfolk Southern Railroad Project

GeoSonics/Vibra-Tech can let you know what lies beneath the surface, even before construction begins.

A seismic tomography survey was conducted by GeoSonics/Vibra-Tech at the location of the existing S.R. 0075 Bridge over the Norfolk Southern Railroad line in Port Royal, PA. The objective of the geophysical survey was to measure the compressional wave velocities of the existing east and west concrete abutment foundations. Compressional wave velocities are an indicator of the strength and soundness of concrete, where higher wave velocities are associated with competent concrete and slower velocities with degraded concrete. Three vertical boreholes were drilled in a triangular pattern through each abutment. At the location of each abutment, seismic measurements were made at various depths in two of the boreholes while the third borehole housed the seismic source. Traveltime information was then inverted using a seismic tomographic inversion scheme to image the interior structure of each abutment. A total of four anomalous zones – zones of lower velocity (<6,000 ft/sec) – were identified in the abutments (two in each). Confirmation drilling encountered zones of degraded/honeycombed concrete at various depths that agreed with the identified anomalous features from the tomography survey.

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