Simulation of GPR response for 2-D and 3-D synthetic models for geotechnical applications, case study: detection of subsurface along Isfahan main power line tunnel

In this research, the GPR method has been employed to identify subsurface in-homogeneities along Isfahan main power line tunnel as an application in geotechnical engineering practices. To this goal, the GPR response of common 2D synthetic models including horizontal cylinder, 2D prism and arbitrary polygon corresponding to targets encountered in usual geotechnical practices were simulated first. To achieve this objective, an improved 2D finite difference algorithm developed for forward modeling in frequency domain, was used in MATLAB programming environment. Next, the GPR response of 3D synthetic models containing vertical cylinder and sphere (representing usual form of cavities) was produced by means of GPRMAX3D software for more detailed and realistic interpretations. To detect probable subsurface in-homogeneities including different types of manmade buried installations, subsidence and buried wells along the Isfahan main electric power line tunnel, 14 longitudinal GPR profiles covering more than 1200 meters along the tunnel axis were surveyed. The data were collected using a 250 MHz GPR system equipped with shielded antennas. The interpretation of final radargrams after applying different filters revealed that the GPR method is capable of detecting the location and type of subsurface in-homogeneities. In order to verify the performance and ability of GPR method in solving geotechnical problems encountered in real geological conditions and in particular the results obtained in current case study, a vertical borehole was drilled at one of in-homogeneities found on the radargrams which had been interpreted as a buried abandoned well. The result was in agreement with the respective interpreted radargram.