This synthesis will be of interest to state Department of Transportation (DOT) geotechnical, bridge, and pavement engineers, engineering geologists, consultants involved with ground penetrating radar (GPR) investigations for state DOTs, and researchers. It describes the current state of the practice of using GPR for evaluating subsurface conditions for transportation facilities. This was accomplished by conducting a literature search and review and an extensive survey of U.S. and Canadian transportation agencies and practitioners, as well as limited international information collection. GPR is a noninvasive nondestructive tool used in transportation applications such as evaluation and characterization of pavement systems, soils, and environmental problems. This report of the Transportation Research Board presents information on the principles, equipment, logistics, applications, and limitations of GPR pertaining to transportation applications. Selected case studies for which ground truth information is available are presented. In addition, an extensive bibliography and glossary are provided as well as appending information about GPR manufacturers from their literature.

Subsurface drainage features are routinely incorporated in the design of pavement systems as they are believed to increase pavement service life provided that they are installed correctly and maintained. Maintenance, however, is challenging in that location and subsequent inspection of these systems can be time consuming and laborious. With this in mind, some departments of transportation have turned to ground penetrating radar as one means to rapidly locate subsurface drainage features in pavements and thus alleviate some of the cost and complexity of maintaining these systems, but with mixed results.In this context, this study pursued a two-pronged approach to improve GPR-based location of sub-pavement drainage systems, involving: (1) software-based signal processing and (2) modifications of hardware test configurations. From a signal processing perspective, two complementary signal processing approaches were developed in this work. Method 1 involved algorithms that are designed to reduce GPR signal background clutter and noise by taking advantage of the somewhat uniform nature of the strata underlying constructed pavements and to systematically remove anomalous signals. Method 2 focused on enhancing 2-D image quality to facilitate recognition of hyperbolic signal returns indicative of drain detection. From a hardware perspective, field experiments were also carried out in this work to validate the signal processing algorithms and assess the potential for alternative antenna configurations to enhance detection success. Five different antenna configurations were tested in total. When employed in field settings, the signal processing algorithms demonstrated an ability to routinely detect X-drains (shallow depth, PVC) with 2-3 false alarms per successful detection. Similarly, all known K-drains (moderate depth, metal/clay) in the studied field test regions were successfully identified, although each successful K-drain detection was accompanied by a significant number of potential false alarms. Beyond these signal conditioning related findings, additional recommendations for field deployed GPR survey line selection, antennae configuration, and frequency selection are also provided.

This report will describe the various kinds of information that can be obtained from roads and highways with Ground Penetrating Radar. In the last 5 years, attention has focused on measuring the thickness of the asphalt surfacing layer on flexible pavements with air-launched horn antennas. Other antennas are available with substantially different depths of penetration, and for use in a wide range of other pavement applications. The purpose of this report is to describe the range of applications of GPR in pavement evaluation. Cases include subgrade investigations, bedrock evaluations, locating sinkholes, detecting frost damage, and identifying defects such as stripping or voids and monitoring crack growth within the pavement structure. The large variety of cases, conducted in Texas and Finland, illustrates the unique ability of GPR to rapidly evaluate subsurface conditions. The sinkhole detection study represents our initial effort to use low frequency deep penetrating radar on Texas pavements. A unique feature of this paper is the proposed classification of the frost susceptibility of subgrade soils by their measured dielectric constant and electrical conductivity.

The research project objective was to develop an implementation strategy for the use of Ground Penetrating Radar (GPR) technology to address pavement systems and underground utilities. The project was divided into three tasks. Task 1 dealt with a review in the state-of-the-art in technology, relevant applications, and regulations in the use of GPR. Task 2 discussed the effort and results of GPR survey projects on pavements systems and underground utilities that were performed as part of this project in selected locations. Task 3 developed an implementation strategy for NYSDOT for defining and procuring GPR services in addressing problems in pavement systems and mapping & locating underground utilities.