Infrasense, Inc., a national leader in infrastructure nondestructive evaluations, recently completed an analysis of GPR data from Burnie Port on the northwest coast of Tasmania, Australia. For this project Infrasense, Inc. partnered with GPR Imaging Solutions of Melbourne, which was formed in 2013 to introduce high speed subsurface scanning into the Australian market. GPR Imaging Solutions collected the GPR data, while Infrasense analyzed the data. Infrasense has previously collaborated with GPR Imaging Solutions on several projects related to the evaluation of pavement structures.
A section of the port was built on reclaimed land about 50 years ago. The pavement on this port is generally up to 300mm of asphalt over a crushed rock base. Moisture in the crushed rock and voids/cavities are known to exist below the asphalt initially discovered by coring. This knowledge created concern for the port manager who requested this project to determine the extent of these problems and possibly determine an approximate depth of the problem areas below the asphalt.
GPR Imaging Solutions collected GPR data in 4 areas to detect voids and areas of high moisture. The data was collected with a combination of a 1GHz horn and a 400MHz ground-coupled antennas. Due to obstructions and to minimize disruption to normal port operations, the data was collected in an irregular pattern, but by using GPS the location of detected voids could be spatially referenced. Over 80 data files were collected in this fashion. Infrasense, Inc. used an amplitude-based analysis to identify areas where voids and high moisture content were likely at different depth ranges.
The results of this analysis were used to create GPS coordinate-based plan area contour plots showing the void and high moisture locations overlaid on top of aerial maps of the port. The figure above shows a sample of one of the maps. The blue-magenta color scheme refers to conditions in the 500-1000 mm depth range and the green-orange color scheme refers to conditions in the 1000-1500 depth range. As was demonstrated on this project, GPR is a very useful tool in planning preventative maintenance and avoiding severe and costly structural issues down the road.