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What is an underground utility survey?
Why carry out underground utility surveys?
What techniques are used?
What results can be expected from a survey?
What are the limitations of a survey?
What level of survey do I require?
Further questions
What is an underground utility survey?
This is the process of carrying out both desk-based and site investigations using a variety of non-intrusive techniques to provide accurate plans of the buried utilities within a specified survey area.
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Why carry out underground utility surveys?
Many benefits arise from having good quality mapping of the buried utilities of a site, including:
- Ensuring safety of both the public and the workforce during construction work
- Minimising cost and disruption arising from damage to existing utilities
- Minimising project delays
- Optimising designs of new works by knowing the constraints of the site
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What techniques are used in carrying out these types of surveys?
Several technologies can be used to obtain information on the position of buried pipes and cables. Each will have a varying degree of success and accuracy in a given environment. When performing an underground survey it essential that the appropriate equipment and methodology is used in the best way for the given situation. Each will find some pipes and cables in some situations, whereas, with an educated approach, most if not all utilities can be accurately determined in a wide variety of situations. The two most commonly used techniques are radiodetection locators and ground penetrating radar (GPR). SafeGround operators have many years’ experience with both techniques to bring you the best survey solution.
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What results can be expected from a survey?
At the end of this document is a summary of the different levels of survey that are suggested to satisfy the various client requirements for utility tracing and mapping. Though ‘mark out’ on site may be appropriate in some instances, it is recommended that the results be provided as plots onto accurate base mapping. We can provide a range of drawing formats including CAD, DXF and DWG.
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What are the limitations of a survey particularly concerning accuracy and depth of investigation?
Some of the main criteria affecting the success of a survey will be the site conditions, the sub-soils and the depth and type of utility being surveyed. As long as these factors are not too constraining, positional and depth accuracies of around 50–150mm can be expected down to a depth of 1.5–2m. It is possible to detect larger utilities at greater depths. It must be appreciated that radiodetection will not detect non-metallic utilities whereas GPR should pick up most material types.
However, even with a full comprehensive multi-technique level 6 survey, we cannot provide a 100% guarantee that every single utility has been detected. No company can provide this without undertaking costly multiple excavations. However, we do ensure that every effort has been made to locate the buried services and obstructions using a range of techniques to provide you with the means that all reasonable care has been taken.
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What level of survey do I require?
The schedule below is a simplified version of a comprehensive table showing more options and listing the limitations of each type of survey.
- Level 1 A desk-based search of utility company records with the results consolidated onto base mapping. This is offered as part of our desk study
- Level 2 Using just a radiodetection tool search in active and passive modes with located utilities being marked out on the ground surface only
- Level 3 A level 2 survey but the results plotted onto digital base mapping in CAD
- Level 4 A level 3 survey but with lifting of manhole and inspection pit covers etc. recording the contents and noting tracing the lines of pipes and ducts using radiosondes or tracing rods. Results produced digitally in CAD
- Level 5 A level 4 but with a predefined percentage of the survey area covered with close-centred recorded radar transects. This radar data to be post-processed and interpreted at a later stage for incorporation into digital mapping along with the level 4 data.
- Level 6 A level 1 and level 5 survey combined but with 100% coverage of the survey area with close-centred recorded radar transects. This is the highest level of survey and is covered by our utility mapping service.
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Further questions
We are always happy to advise on principles and techniques. To discuss the benefits of a well-designed and well-executed survey, please feel free to contact us for more information.
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