Subsurface Utilities Part 2 - The Capture & Recording, Bennett and Bennett

Subsurface Utilities Part 2: The Capture & Recording


Continuing from last week’s article on ‘Underground Services – Field Location Methods’ (Part 1 of our 3-Part series), we summarise the Australian Standards for the recording of underground services and their various classifications.

The level of detail and accuracy you will need is dependent on what stage of the development you are at, balanced by the need to provide sufficient data to your design team.

Classification of Subsurface Utility Information (SUI)

Australian standards have been developed to provide a consistent framework for the classification of information concerning underground services. They are separated into 2 parts:

  • Part 1: AS 5488.1:2019: Primarily deals with location of the assets
  • Part 2: AS 5488.2:2019: Utility model creation and data naming conventions and survey engagement

Standard colours (see below), line types and quality levels are some of the national standards you may see represented on our survey plans. These help in minimising confusion and misinterpretation by the end users of the data.

Subsurface Utilities Part 2 - The Capture & Recording, Bennett and Bennett

Bennett + Bennett Standard Colours representing utilities.

Quality Levels

Each of the sources that contribute to service location have varying levels of accuracy. By implementing ‘Quality Levels’, users are able to recognise the underlying accuracies and make informed decisions about the service and avoid injury or damage. There are four accuracy levels (A, B, C, and D). You will note underground service alignments shown on Bennett and Bennett plans make a reference in brackets to these 4 levels of accuracy.

Starting from the lowest quality level QL-D and finishing at the highest level QL-A as follows:

Quality Level D (QL-D) – lowest level

  • Accuracy: Very low and is only shown indicatively.
  • Risk Involved: Very high risk of damage.
  • Main Uses: Used to establish the potential presence of a utility within an area of interest for general project planning and concept design.
  • Utility information may be sourced through a variety of methods including but not limited to DBYD utility records, GIS databases, existing records, personal recollections, and cursory site inspections etc. The assets are not field verified and may be in a schematic format only and intended to indicate their presence or they could be positioned from boundary offsets or scaling.

Quality Level C (QL-C)

  • Accuracy: No Vertical accuracy; Horizontal accuracy of ±300mm.
  • Risk Involved: High risk of damage
  • Main Uses: Builds on QL-D quality levels with improved horizontal position for more refined project planning and concept design.
  • Utility information is a combination of data from existing records or GIS databases and is adjusted to suit visible evidence at or above the ground surface. e.g. pit lids shown on plans are evident on site however the underground connection between the lids is still assumed. There is risk that the underground connections are not simple a straight line between and may deviate or have bends between the pits.
Subsurface Utilities Part 2 - The Capture & Recording, Bennett and Bennett
Subsurface Utilities Part 2 - The Capture & Recording, Bennett and Bennett

Quality Level B (QL-B)

  • Accuracy: Vertical accuracy of ±500mm; Horizontal accuracy of ±300mm.
  • Risk Involved: Significant reduction in risk.
  • Main Uses: Used to further advanced design, project planning and route selection for new infrastructure.

Utility information is generally plotted from any certified service locator methods such as EMF, GPR, acoustic pulse equipment, or sondes etc. These methods are often affected by soil conditions, interference from electromagnetic fields, and generally do not account for multiple banks of conduits or cables.

Quality Level A (QL-A) – Highest level

  • Accuracy: Vertical and Horizontal accuracy of ±50mm.
  • Risk Involved: Minimum risk.
  • Main Uses: Fills in any gaps or shortfalls from lower quality levels and finalises construction documentation ready for project delivery.
  • This is considered the ‘highest standard’ for locating as it provides the highest level of accuracy. To achieve this quality level the underground utility is physically surveyed when initially installed prior to backfilling or exposing via non-destructive digging such as potholing. Rich attribute data such as type, material, condition, size and other relevant characteristics can be captured to assist with precise project planning. This is the only quality level that ‘validates’ an underground utility.

Often potholing will only provide ‘positive identification’ at a particular point along the utility so any underground connections (line segments) between potholes that cannot be verified by line of sight will not be able to apply the QL-A quality level.

All projects are different and due to time or cost constraints it is not simply practical to utilise QL-A quality levels on every project. A combination of QL-B, QL-C and QL-D may be suitable for the project brief pending size, scope and management of associated risk within the project.

Subsurface Utilities Part 2 - The Capture & Recording, Bennett and Bennett

You can purchase the Australian Standards (AS 5488.1:2019) for the classification of underground services online through this link – AS 5488.1:2019.

Look out for Part 3 (of our 3 Part series) on the ‘Enhanced Data delivery options for Underground Utility Surveys’ coming out next week.

Bennett + Bennett work closely with certified service locators and vacuum excavation companies and can assist with formulating an underground services proposal to assist your project brief.  If you have any queries  please contact us via phone 07 5631 8000 or email [email protected].

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