Investigation of long term moisture changes in roadbeds using GPR

The paper is dedicated to development of a method of assessing the moisture content in a subgrade that has been exposed to occasional rainfalls and seasonal weather effects. The method is based on the obtaining and processing GPR data and allows to investigate long term moisture changes in the railway roadbeds. The change of the signal shape with time is considered depending on the attenuation of electromagnetic radiation in the medium and its reflection from the soil layers boundaries. To analyze the soil moisture content the integral reflectivity as a quantitative characteristic is proposed in this method. This variable is used to evaluate the moisture changes under rainfalls and other seasonal factors. The method verification is performed using RAW data of GPR profiling of Tuapse-Adler (Russia) railway section in December 2009 and between May and September 2010. It´s shown that the value of integral reflectivity is sensitive to the soil moisture. Thus the dynamics analysis of changes in soil moisture on the selected railway sections depending on the different seasons is made. These results are in good agreement with data obtained by a track recording car.