GTS Technologies -- Geophysical

On a Saturday morning in January 2004, GTS Technologies was contacted by the Pennsylvania Department of Transportation concerning a potential bridge collapse that closed the S.R. 0033 Northbound Bridge over the Bushkill Creek just north of Allentown, PA. The task required determining the extent and severity of sinkhole activity in and around the existing S.R. 0033 Bridge locations. Due to the closing of the northbound structure, it was imperative that quick action be taken to determine the impact of sinkhole activity on the remaining southbound bridge and assess the severity of the problem at the northbound structure.

GTS Technologies assembled their team of highly experienced geologists, geophysicists, and engineering technicians and mobilized to the site within a few hours of being summoned. The team preformed a site reconnaissance, assessed the situation and began preliminary geophysical work using our AGI R-8 Supersting resistivity equipment. Preliminary geophysical studies, and GTS's previous involvement in similar work within the area, suggested a larger geologic problem. This information along with supporting evidence was presented to the Department within a day of completing the preliminary geophysical survey. Recommendations and options for further in depth, highly advanced studies were provided to the Department for consideration.

The geophysical team assisted and advised the Department of the potential geophysical techniques, associated costs and benefits (as well as limitations), to devise an effective and encompassing subsurface investigation.

GTS Technologies used a 56-electrode resistivity array along with seismic refraction techniques combined with exploratory core borings to investigate and quantify subsurface conditions to depths approaching 180 feet below the surface. The results of the investigation showed where the Bushkill Creek was actively eroding the raveled bedrock beneath the existing bridge substructures and identified where favorable subsurface conditions existed. Due to GTS's geophysical and geotechnical expertise, as well as quick emergency response, the Department maximized their subsurface information to determine the type, dimensions and location of the replacement structures.