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Utility services detection

Common geophysical methods:



Utilities mapping service

Utility services surveys typically comprise of a combination of the following:

  • Review of available utility plans 
  • Tracing of identified utilities
  • CCTV surveys of drainage
  • Marking out identified services on site
  • Detailed topographic surveys
  • Visual inspection of access chambers
  • Scanning survey area to identify unrecorded utilities
  • GPR scanning to detect non-metallic utilities
  • Mapping of in-ground structures
  • Integration of existing plans

Important aspects

Issue  

Comment

Are the specified targets of interest detectable?

The detectability of any buried target is a function of its size with respect to depth of burial, its material composition, and its burial setting. For example, a plastic water pipe may be detectable in sandy fill materials but may be invisible in a clay-rich burial setting or beneath double-reinforced concrete.

What are the limits of detection constraints for real-time versus recorded surveys?

Real-time surveys are practical for most RFL applications but only useful for GPR in low density services environments.

Single channel GPR versus multichannel GPR

Multichannel GPR when deployed in recorded surveys can increase the probability of detection to over 90% compared with 70% for single channel GPR surveys assuming suitable burial settings.

How important is survey design in delivering cost effective results?

Design of a geophysical survey including selection of appropriate scanning methods and effective survey coverage required is the key aspect determining the likelihood of success.

Have survey limitations been discussed in the context of the specific site?

No survey design can be considered robust without formal consideration of expected in-situ materials and the burial setting of the targets.

How important is site access to deliver an accurate and comprehensive map to budget?

Partial detection of services in busy, high density services areas can result in ambiguous and incomplete maps. Access constraints can also significantly increase the time on site required to complete the survey.

Is the service provider a licensed member of EuroGPR?

Operation of GPR without a valid Ofcom license is illegal.

How experienced are the site technicians? Will data processing be carried out by office-based staff only?

Utilities mapping is a specialist skill. Even an expert geophysicist without practical utilities identification experience will deliver an inferior product compared with a trained geophysical technician with experience tracing services in the built environment. The input of site personnel in preparing maps and QC’ing map deliverables is vital.

 

Zetica Test Site

Zetica has constructed a unique utility services area at its test site.  This facility represents a host of real-life scenarios in which utility services detection may be required. It includes conducting and non-conducting services buried at various depths beneath undisturbed soil, made ground, unreinforced concrete, and reinforced concrete (single and double reinforcing layers).  There are also varying sizes of air- and water-filled voids at depths up to 0.5m below ground level. Metal plates for calibration are also buried to 1.2m below various ground cover types.

The test site provides a facility for training staff in a controlled environment and for introducing customers to technologies and processes.  It also enables Zetica to evaluate the effectiveness of a range of methods and new equipment.  This provides Zetica’s clients with the added confidence that the stated limits of detection are based on practical and not just theoretical assessment.    

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