Over the past few decades, advances in technology has allowed electronics and computers in general to become more portable and to be able to store more data than ever before. Ground Penetrating Radar (GPR) is a non-destructive technology that is typically associated with archaeological studies, but has recently become more prevalent in civil engineering field with applications ranging from subsurface utility detection to structural concrete assessments.
The principle of GPR technology is based on the reflection/transmission of microwave electromagnetic energy and recording its response to different materials, which are governed by two physical properties of the material; electrical conductivity and dielectric constant. For reflections to occur at different material interfaces, there must be a contrast in dielectric value (reflection produced at a boundary where the dielectric value changes). During subsurface material/void detection, depending on the size of the target, there will generally be a distinct reflection due to the contrast in dielectric between the subsurface materials and the target structure.
Generally, GPR data is collected using two types of systems: air-coupled and ground-coupled systems. Air-coupled systems are typically vehicle mounted and use an antenna frequency between 1.0 to 2.0 GHz which is capable of a depth of penetration ranging from 0.75 m to 0.9 m below the ground surface. There are a large variety of ground-coupled systems, but typically are mounted using a cart with single, or multiple wheels depending on the size of the antenna and must have constant contact with the surface being scanned. Antenna frequencies range from 16 to 2,600 MHz with depth of penetration ranging from 0.3 m to 50 m.
This paper presents several case studies using both air-coupled and ground-coupled GPR systems in pavement engineering applications ranging from void detection, Species at Risk (SAR) investigations, subsurface utility/structure detection and concrete reinforcement detection.
The results of the case studies show that GPR is a non-destructive data collection method that can be used in several different ways to collect a large amount of data over a large area relatively quickly compared to typical investigation methods (coring or drilling). It is important to understand the limitations of the equipment (signal penetration, size of target, etc.), as well as the appropriate system to use in a specific situation (air-coupled vs. ground-coupled). Ground truth data was also critical in the data analysis and interpretation of the GPR scans. Additionally, using the utility survey cart-mounted antenna in a cross-polarized orientation aided in capturing data in a steel congested structural element and allowed the GPR engineers to help identify voids.
Korczak, R.
Abd El Halim, A.
