ASTM D6432-19

1.1.1 This guide covers the equipment, field procedures, and interpretation methods for the assessment of subsurface materials using the Ground Penetrating Radar (GPR) Method. GPR is most often employed as a technique that uses high-frequency electromagnetic (EM) waves (from 10 to 7000 MHz) to acquire subsurface information. GPR detects changes in EM properties (dielectric permittivity, conductivity, and magnetic permeability), that in a geologic setting, are a function of soil and rock material, water content, and bulk density. Data are normally acquired using antennas placed on the ground surface or in boreholes. The transmitting antenna radiates EM waves that propagate in the subsurface and reflect from boundaries at which there are EM property contrasts. The receiving GPR antenna records the reflected waves over a selectable time range. The depths to the reflecting interfaces are calculated from the arrival times in the GPR data if the EM propagation velocity in the subsurface can be estimated or measured.

1.1.2 GPR measurements as described in this guide are used in geologic, engineering, hydrologic, and environmental applications. The GPR method is used to map geologic conditions that include depth to bedrock, depth to the water table (Wright et al (1)2), depth and thickness of soil strata on land and under fresh water bodies (Beres and Haeni (2)), and the location of subsurface cavities and fractures in bedrock (Ulriksen (3) and Imse and Levine (4)). Other applications include the location of objects such as pipes, drums, tanks, cables, and boulders, mapping landfill and trench boundaries (Benson et al (5)), mapping contaminants (Cosgrave et al (6); Brewster and Annan (7); Daniels et al (8)), conducting archaeological (Vaughan (9)) and forensic investigations (Davenport et al (10)), inspection of brick, masonry, and concrete structures, roads and railroad trackbed studies (Ulriksen (3)), and highway bridge scour studies (Placzek and Haeni (11)). Additional applications and case studies can be found in the various Proceedings of the International Conferences on Ground Penetrating Radar (Lucius et al (12); Hannien and Autio, (13), Redman, (14); Sato, (15); Plumb (16)), various Proceedings of the Symposium on the Application of Geophysics to Engineering and Environmental Problems (Environmental and Engineering Geophysical Society, 1988-2019), and The Ground Penetrating Radar Workshop (Pilon (17)), EPA (18), Daniels (19), and Jol (20) provide overviews of the GPR method.

1.2.1 This guide provides an overview of the GPR method. It does not address details of the theory, field procedures, or interpretation of the data. References are included for that purpose and are considered an essential part of this guide. It is recommended that the user of the GPR method be familiar with the relevant material within this guide and the references cited in the text and with Guides D420, D5730, D5753, D6429, and D6235.

1.2.2 This guide is limited to the commonly used approach to GPR measurements from the ground surface. The method can be adapted for a number of special uses on ice (Haeni et al (21); Wright et al (22)), within or between boreholes (Lane et al (23); Lane et al (24)), on water (Haeni (25)), and airborne (Arcone et al (25)) applications. A discussion of these other adaptations of GPR measurements is not included in this guide.

1.2.3 The approaches suggested in this guide for using GPR are the most commonly used, widely accepted, and proven; however, other approaches or modifications to using GPR that are technically sound may be substituted if technically justified and documented.