Diagnosis of bedrock course and retaining wall using GPR

The paper presents the application of the Ground Penetrating Radar (GPR) technique to the diagnosis of bedrock and a retaining wall. There was a need to repair the retaining wall constructed in 1912. The wall was constructed along a railway track, and its length was about 135 m. Crushed stone and lime mortar were used to build the retaining wall. There were no archival records of its geometry, inspection, or design documentation or geotechnical subsoil studies. Because of the need to define acceptable conditions for its service, it was necessary to determine its shape and stability as well as its foundation. A mountain river flows in the close vicinity of the retaining wall (near its base), and from the slope side on a narrow shelf there is very intense two-track rail traffic on the international main line. It was not possible to conduct traditional geotechnical tests due to the following factors: (i) the extremely difficult conditions preventing the execution of drilling near the wall (with a height of up to 5.0 m) and (ii) the inability to stop traffic on both railway tracks. Using the GPR technique, supported by outcrops and open pits in the vicinity of the wall, which were used as calibrators, it was possible to obtain the important data for the retaining wall design. Conclusions drawn from the tests can be helpful in measurements using the GPR technique, especially for geotechnical investigation of the ballast and bedrock and assessment of the technical condition of the retaining walls.