Quality Assurance Testing at Harbor River Bridge by GRL Engineers Sponsored

The known vacation destination, Harbor Island, is accessed through this drawbridge, located on US-21 in South Carolina. Bridge’s capacity is no more sufficient and the narrow lanes present potential hazards to drivers. The county of Beaufort decided to take action and proposed in 2014 a new design. The new bridge will consist of 12-foot-wide lanes with 10-foot-wide shoulders and will reach heights of 65 feet, allowing clearance for shrimp boats and fishing charters without disrupting traffic.

GRL Engineers performed quality assurance testing on a sacrificial test shaft as was required by the South Carolina Department of Transportation. GRL used the Shaft Area Profile Evaluator (SHAPE) in the slurry-filled hole for verticality and profile analyses. With a visual representation of the shaft, they were able to assess an offset verticality of 0.22 ft. An evaluation of shaft base cleanliness was performed with the Shaft Quantitative Inspection Device (SQUID). Using penetrometers with embedded strain gages and displacements plates, the resulting force and penetration distance into the bearing material formed a resistance vs displacement plot for real-time quantitative assessment of the debris thickness at the shaft base. 

GRL performed Thermal Integrity Profiling using Thermal Wire® cables to assess the concrete quality and concrete shaft geometry along the instrumented length of the shaft. Prior to concrete placement, the TAP-Edge and TAG (Thermal Acquisition Port data loggers) were connected to the Thermal Wires for on-site data collection in the Cloud. An automatic reading was taken every 15 minutes and sent to the cloud for remote analysis. 

GRL Engineers used Bi-Directional Static Load Testing to evaluate load-bearing and capacity 8 days after the shaft construction. An equivalent top-loading (“ETL”) curve was constructed using the load-transfer method. This method indicated that the equivalent maximum top load would be 7,863 kips.

With the bearing and load capacity determined by this test pile, the project’s engineers will be able to make informed decisions based on quantitative data gathered by GRL Engineers. The new bridge is predicted to be completed by the end of 2021.