Subsurface GPR imaging of a potential collapse area in urban environments

Ground penetrating radar imaging is one of the promising nondestructive and noninvasive methods that have offered new opportunities for mapping the subsurface structures of shallow earth in highly urbanized regions. In this study, we performed the ground penetrating radar survey in a potential collapse urban area. The acquired data were processed through the logarithmic transformed ensemble empirical mode decomposition (EEMD) methodology that reduces the exponential decay of the original data and extracts meaningful images. This method proves successful in imaging the top pavement layers, utilities and voids within approximately 2 m depth. Moreover, the quality of the subsurface image can further be improved by using the sub-component EEMD filter bank. Through a control study followed by the general field survey and direct excavations, we demonstrate the efficiency and quality of this method in mapping shallow structures in an urban area. An interpretation of the cause for the collapse in the study area is also proposed.