GEOPHYSICAL FACT FILE
GROUND PROBING RADAR 2
NON-DESTRUCTIVE TESTING
INTRODUCTION
Ground Probing Radar or ground penetrating radar (GPR) is a useful NDT method applicable for testing buildings, bridges, tunnels and retaining walls, and for general concrete testing applications. GPR is non-destructive and non-invasive, revealing a wealth of internal detail without the need for coring or breaking out. Results are presented as engineering CAD plans, elevations and sections.
Ground radar equipment can be adapted for different requirements using interchangeable antenna units. Low frequency antennas locate large steel elements in concrete and find deep-seated voids. Small, hand-held high frequency antennas are best for locating individual rebars and cable ducts, and finding tie bars. High frequency antennas also assess the integrity of reinforced concrete and brickwork, and find small voids, delaminations and other defects.
CONCRETE FLOORS
Ground penetrating radar is an effective concrete testing method for investigating factory floors. GPR surveys can measure the thickness of reinforced concrete slabs and determine the depth and spacing of rebars. Information can generally be obtained through more than one layer of reinforcing mesh. Individual structural elements such as beams and girders can be identified, together with voids, delaminations and other defects not easily found by coring alone. GPR can be especially useful on older, multiple use floors which have been repaired and partially replaced over time. The patchwork of different floor thicknesses and variable reinforcing mesh distribution often presents significant complications to structural engineers. A GPR survey can characterise the floor construction, providing vital assistance for planning the installation of new plant.
Ground radar profile of beams below a double mesh reinforced concrete floor
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RETAINING WALLS
Ground penetrating radar surveys can be customised to investigate concrete or masonry retaining walls, to produce profiles of the wall thickness. Voids and other defects can be identified both within the wall and behind the internal boundary of the structure.
Vertical profiles are carried out by lowering the antenna down the external face of the retaining wall. Horizontal profiles are useful for identifying lateral changes in thickness, particularly if a buttress type construction is suspected, and for defining the extent of a large defect. The interpreted data is used to construct elevations and sections of the wall's internal construction.
SEA DEFENCES
Sea wall GPR investigations can assist engineers for breach detection and structural assessment. Breach detection involves surveying the ground immediately behind the sea wall, to look for voids and loose ground caused by marine incursions into the wall. For structural assessment applications, GPR surveys can produce typical wall sections for structures where records no longer exist.
Generally ground radar surveys are best commissioned prior to the commencement of major renovation programmes. The results can be used for targeting costly remedial operations and the early identification of potential failure zones.
BRIDGES & TUNNELS
Ground radar surveys are used on bridge structures for assisting load assessments and as a follow-up to routine inspections. A GPR survey is able to locate internal defects for theaccurate targeting of intrusive investigations.
On masonry arch structures, GPR is used to check barrel thickness, locate defects and identify backing on the haunches of the arch.
GPR investigations of reinforced concrete structures check slab and element thickness, measure rebar spacing and can assess the condition of internal steelwork.
GPR APPLICATIONS
- Investigates thickness and internal structure of floors and walls
- Locates internal steelwork in concrete such as rebars, girders & cable ducts
- Identifies backing behind masonry arches
- Locates voids, cracks and delaminations in concrete and masonry
- Finds zones of water penetration and corrosion within defective concrete
- Determines thickness of brickwork and masonry construction layers
(C) 2009 SUBSURFACE GEOTECHNICAL