An overview of Ground-Penetrating Radar (GPR)
Ground-penetrating radar (GPR) technology is a nondestructive testing device used in various fields of civil engineering specially for determining sub surface utilities. Waves of various frequency bands are radiated into the ground by the transmitters and then are reflected back to the receivers. Using the acquired signals, the location and shape of the subsurface anomaly can be determined. GPR has been used in several research projects and practical engineering application for various purposes such as in boreholes where the GPR is used to characterize the ground mass, soil fractures, infill and soil hydraulic properties. It has also been used in the identification of soil water content detection of voids and sinkholes, evaluation of the ground structure around tunnels and linings, foundation assessment and identification of foundation strata, location and identification of underground utilities, inspection of road pavement, railway subgrades and ballast characterization and bridge deck condition assessments.
Working of GPR
- A transmitter (Tx) produces electromagnetic impulses at a high repetition rate which are transmitted through the ground.
- Reflections occur where the electrical properties of materials change.
- These reflections are detected by the GPR receiver (Rx) and displayed on a monitor.
Subsurface features, which may cause such reflections include:
- Man made objects such as utilities, i.e. cables and pipes (metallic and non-metallic).
- Underground Storage Tanks (UST).
- Road construction…material layers.
- Natural geologic conditions such as changes in soil composition, supporting layers, ice, groundwater table, bedrock, boulders, voids and more.
Reflection Strengths from Various Materials
GPR for Utility Detection
- GPR detects metallic and non-metallic utilities including plastics, concrete, and other non-conductive lines.
- Most common utilities essential for deployment of GPR are water, gas, and sewer.
- Great tool for prospecting site for unknowns.
Depth Estimate Techniques Include
- Hyperbola Matching
- Estimation of Soil Velocity and/ or Dielectric Value of the soil
- Scanning over a known target and adjusting GPR response to the appropriate depth.
After carryout the GPR survey, all the data collected are process with PC-based software and plans, profile with elevations are produced. These can be further categorized by type, depth etc. as per requirements.
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