Searching and Measurement of Functional Voids by Means of Gpr Tomography by the Example of Two Columns

The present article focuses on GPR tomography method potential aimed at the search of functional voids and estimation of their sizes in engineering structures. The size of voids is assumed to be greater than the wavelength for usable frequency. Two examples of the GPR tomographic survey are examined: 1) a square con-crete pillar with granite coating and a square void in the center, 2) cylindrical granite column with functional spherical void which has iron walls. The following issues are considered in the article: the method, the structure of the acquired data, the picking of wanted waves, the analysis of tomographic inversion result, compared with the result of commonly used single-fold antenna geometry GPR. As a result of the research performed it was demonstrated that GPR tomography represents a good solution for the problem of detection, delineation and characterization of voids inside engineering structures. The velocity of electromagnetic waves propagated within the solid part of the column (concrete and granite) was accurately measured. The measured velocity can be con-sidered to the basis for physical properties estimation, for example humidity, voids ratio etc. The acquired quan-titative results are characterized by high quality and are more reliable compared to the results of single-fold GPR survey.