Overview

Ground penetrating radar (GPR) is a geophysical survey Technique and the main component of a PAS 128:2014 for utility detection and mapping survey.

GPR is:

A geophysical- approach that is, precise, fast and high-resolution for subsurface investigation.

Non-invasive, non-destructive and completely safe procedure.

One and only possible non-intrusive method capable of accurately locating non-metallic subsurface features and utilities (example- clay, concrete, fiberglass, PVC conduits or fiber-optic cables).

A geophysical survey technique based on transmitting pulsed electromagnetic (EM) energy into the subsurface and ascertaining the strength of the reflected energy.

Effective in case enough contrast in material properties (dielectric permittivity) between a buried target and its surroundings exists.

Applied by Epitome in order to detect and map buried pipes, cables, structural reinforcement, voids, disturbed ground, material degradation, subsurface layers and buried objects.

Gained by use of transmitting and receiving antennae which can be mounted on a cart, skid plate or vehicle, or can be hand-held.

A technique that allows skilled and experienced personnel to attain distinct survey data and geophysical expertise to process and interpret the results.

GPR METHOD

Ground Penetrating Radar operates by transmitting high-frequency radio waves pulses down into the ground through an antenna. Ground Penetrating Radar is distinctly able at not only mapping buried structures but also relatively measuring their depth, and supplying an all-important thorough detail.

The antenna is moved over the surface to be inspected. The transmitter redirects a diverging beam of energy which is reflected in various underground objects or different contacts between different earth materials.

The radargram measured on the vertical scale is in units of the two-way travel time, that’s the time taken by the EM wave to travel down to a reflector and back to the surface. The travel time then is transformed into depth by relating it to on-site measurements or assumptions about the velocity of radar waves in the subsurface material under investigation. Radar wave speeds vary between 60–175 mm/ns for most geological materials.

GPR waves can travel almost 30 meters deep in low conductivity material, as in case of dry sand or granite. Clays, shale, and other high conductivity materials may lessen or absorb GPR signals, leading to the reduction in depth of penetration to 1 meter or less. The GPR antenna can determine the depth of penetration as well.

The selection of antennae is based according to the depth of interest and the size of the target. Penetration depth varies in contrast to the frequency. The higher the central frequency of antenna, the smaller will be the object size to be resolved. Higher antenna frequencies give higher resolution, but less penetration, and vice versa. The lateral and vertical resolution of the results varies from 0.01 to 1.0 meters, as per the choice of antenna frequency. Use of antennae having lower frequency in geological mapping is done to obtain the maximum penetration depth while higher frequencies are used in non-destructive testing for high-resolution imaging. Having a range of frequencies available (usually 50MHz–2.5GHz) makes GPR most suitable for identifying objects of different sizes at different depths and under different ground conditions. We are one of best Ground Penetrating Radar Survey Services, Best Underground Utilities Survey Services and GPR Survey Service in India.

Ground Penetrating Radar Survey Applications

Utility Detection and Mapping

Detect and figure out buried structures including utilities, foundations, reinforcing bars, cavities, tombs, archaeological artifacts, and animal burrows. Subsurface piping leak detection and leak impact assessment (presence of washouts or voids). If you are looking for Ground Penetrating Radar Survey Services, Best Underground Utilities Survey Services and GPR Survey Service in India then you are at the right place.

General Site Investigation

GPR is a non-destructive, surveillance tool for general sub-surface mapping (soil/rock horizons, depth to water table etc.) and locating buried objects prior to invasive investigation.

GPR is useful in the planning and location of follow-up intrusive sampling programs (trial pits, boreholes, coring).

Road & Rail Investigation

Mapping asphalt structure and concrete pavement, for better maintenance and rehabilitation decisions

Identifying and locating voids and zones of construction degradation (concrete layer thickness and water content)

Quality Assurance Control of new structures or existing constructions for rehabilitation purposes

Quality Assurance Control of new structures or existing constructions for rehabilitation purposes

Concrete Non Destructive Testing

Establishing and locating embedded structures (metallic and non-metallic conduits, rebars and tension cables) within concrete structures (e.g., bridges, dams, reservoirs, foundations, tunnels, runways etc.).

Identifying and locating voids and zones of construction degradation (concrete layer thickness and water content)

Quality Assurance Control of new structures or existing constructions for rehabilitation purposes

Quality Assurance Control of new structures or existing constructions for rehabilitation purposes

Road & Rail Investigation

Mapping asphalt structure and concrete pavement, for better maintenance and rehabilitation decisions

Mapping railroad ballast thickness

ldentifying embedded utilities.

GPR Limitations

GPR performance is specified as per the site and it is not suitable for use at some locations. Certain things needs to be taken into account like expected subsurface conditions, target composition, location and size like any other geophysical technique.

GPR anomalies depend on a detectable contrast in subsurface electrical properties between the target of interest and its surrounding material. No anomalies can be detected in absence of detectable contrast

GPR survey not possible at certain places where GPR signal cannot penetrate through highly conductive material e.g., beneath metal sheets or very wet ground or in material saturated with salt water or highly conductive fluid.

GPR is not suitable to absolute measurement, e.g., it can locate wet areas, but not able to determine the moisture content therein.

GPR is an interpretive method, based on the identification of reflectors, which is not helpful in uniquely identifying an object. Additional constraining information from ground truthing or other geophysical methods is important to help resolve any ambiguities.

Like other geophysical methods GPR is intrinsically limited by decreasing resolution with depth.

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