Features of a Large-Scale Survey of Highways with Georadar

The study is based on the results of a georadar study of the pavement substructure obtained during a large-scale geophysical project. The survey consisted of 6000 km investigation of highway pavements and underlying granular layers down to the depth of 0.9 m. It was carried out at high speed (not less than 80 km/h) in order to avoid interference with traffic and using air-coupled (horn) antennae (with center frequency of 1 and 2 GHz). The claim of the regulator for high-speed measurements on highways contradicts is its demand for the acquisition of high-quality data (the required inaccuracy in determining the layers’ thickness had to be less than 8%). The reason for errors could be irregular changes in antennae height during surveying at high speed, changes in the pavement temperature and moisture content, variation in the properties of the pavement due to differences in age, design, and repair history. A common way to reduce the error is to correlate georadar data with the data obtained from control boreholes. However, this method makes the project very destructive, expensive, and time-consuming. In our case, the regulator allowed no more than 100 control wells implying one control borehole per each 60 km of highway pavement substructure. Here we present a methodology for correcting several causes of the inaccuracies in data processing noted above. This methodology includes compensation for irregular drift in antenna height that occurs during high-speed imaging, as well as changes in temperature and humidity. Our extensive study of asphalt cores has shown that the coefficient of dielectric constant can be used to compensate for changes in dielectric properties due to temperature variation. It was shown that the application of the Rayleigh model is very useful for compensating for changes in the moisture content of the pavement structure. The research results presented here make it possible to compensate for inaccuracies in the processing of georadar data and, hence, remain within the accuracy established by the regulator.