GROUND RADAR

Ground Penetrating Radar Surveys:-

Ground penetrating radar (GPR) is a geophysical method which can be used to obtain almost continuous data from the sub-surface or from within a structure. It is often used by a single operator and can be hand pulled or towed behind a vehicle. A GPR unit consists of a power source, data processing unit and a variety of antennae, depending upon the depth and resolution required. Bentham Geoconsulting have invested in the latest SIR 3000 radar system and processing software from GSSI of the USA. Our recent work has included locating voids under a large car park, assessing concrete chimney stacks at a UK petroleum refinery and locating wash-out under the quayside at a northern UK port.

GPR operates by propagating electromagnetic pulses into the ground or structure. Where there is a change in the type or proportions of material then some of the pulse energy is reflected back to the receiving antenna. The processing unit samples the return pulse and depicts the degree of reflection using a predefined colour chart. As the system is moved along the survey line a 2-D image is built up showing the changes in the reflected energy. A survey normally consists of a grid of survey lines so that a full site or area interpretation is possible and the extent of sub-surface material changes becomes apparent.
The photograph to the right shows a radar survey being undertaken on a concrete chimney from a cradle at 112m height.

Ground Penetrating Radar Concrete Chimney Stack Inspection

To a skilled geophysicist the data can be interpreted in-terms of engineering or environmental information. After processing the anomaly patterns are usually shown on an image map and can be used to plan intrusive investigations or simply as a means to avoid existing structural elements during refurbishment.

The image below shows processed data obtained over a 1m x 1m test panel used to show the configuration of steel reinforcement within a concrete chimney stack at a UK refinery.

Applications:-

Concrete chimney stack inspection
Underground storage tanks and interceptor installations
Concrete slabs - voids, reinforcement
Foundation engineering
Buried drums and waste
Tunnel lining inspections
Forensics
Geology
Pollution