Knowing precisely where utilities/services are positioned below the ground surface is important to ensure design, maintenance, or construction activities for new or existing developments & Infrastructure Projects and can be performed safely and efficiently to avoid unnecessary delays to your project. The below outlines different methods of locating underground services and how a surveyor can assist by recording their position.

Mechanical excavators undertaking site works can easily damage existing underground services that are un-documented or shown on a plan in the wrong position. Damage and loss of service due to a rupture can lead to network disruptions/outages and penalties may be imposed upon the person causing the damage. A rupture or strike of an underground asset such as a natural gas pipe or high voltage electricity cable can lead to serious damage to structures and potential for serious injury or death to workers.

what to avoid…

Most of Australia’s major infrastructure asset owners have records of where their infrastructure is located and can be searched via a Dial Before You Dig (DBYD) search avenue. This will usually supply infrastructure located within the road reserve and some public owned land; however, their records are negligible over private land. The infrastructure plotted on asset owners plans may be indicative, incomplete, in the incorrect position, or unable to be interpreted.

It is advised that you do your due diligence on a project that involves Service Location or Non-Destructive Digging such as potholing methods to verify their position.

Let us explain the onsite service detection options:

Survey – Laser Scanning
Certain structures such as sewer and stormwater manholes may be too deep, or they may have chambers that are too complex in shape to accurately be surveyed without having confined space entry. In these situations, it is possible that a laser scanner can be lowered down into the structure to undertake a laser scan survey and capture a point cloud model of the structure itself and any pipes or conduits entering the structure. Very accurate measurements can be extracted from the survey that can show the pipe diameters, invert levels, chamber size and even direction of the pipes leaving the structure.

Service Locators
Certified service locators can use a variety of methods to plot all types of underground services within an area of interest. Methods generally consist of Electromagnetic Field (EMF) technology, Ground Penetrating Radar (GPR), or Push Camera CCTV inspections. Service Location does not involve digging of the ground so is less invasive than potholing and is generally undertaken in the first instance to identify what services are in the ground. Any shortfalls of service location can then be briefed up for a more exhaustive potholing exercise.

Electromagnetic Field (EMF) Locating

EMF location is the most common form of service location and is used on assets containing conductive materials such as steel and copper. The service locator induces a radio frequency onto the asset which the signal is then carried by the conductor along its length and then detected above ground with a radio frequency antenna. Usually for Electricity & Communication lines.

Ground Penetrating Radar (GPR)

Non-metallic materials such as PVC, Asbestos cement (AC) and Polyethylene (PE) cannot be located with EMF and instead we rely on the GPR method to locate non-metallic assets. GPR is a radar technology that transmits an electromagnetic wave through the soil. When the waves encounter an object in the ground, they reflect the wave back to a receiving antenna which records the data. GPR is a good tool for sweeping areas and searching for any undocumented services. For Drainage, Water (recycled & Potable), Fire services, Sewer, Gas & similar services. Vehicle mounted GPR systems are also available to scan for subsurface features while travelling at speeds of up to 100km/hr, allowing for efficient coverage of large areas of pavement.

Push Camera Closed-Circuit Television (CCTV) Inspections

CCTV push cameras are small enough to be placed inside pipework such as sewer and drainage pipes and are perfect for examining the condition of that pipework. They can be moved along the inside of the pipe whilst simultaneously recording clear video imagery that can show for example cracks in pipes, damage due to tree roots, or where pipes intersect other pipes. The CCTV records chainages and depths and these can be related back to any points of interest.

Non-Destructive Digging (NDD)

Non-Destructive Digging is the method used when physically digging and exposing services via either hand digging or more commonly using a vacuum excavator truck to undertake potholing or strip trenching.

Vacuum Excavation (or Potholing)

Vacuum Excavation is a method of removing soil with a high-speed suction directly down on top of the service from a specialised vacuum truck unit. Either air or hydro vacuum excavation can be used for potholing however hydro Vacuum Excavation is the most common whereby pressurised water breaks away the soil which in turn is sucked up by a large hose and stored in a large tank on the truck. Vacuum Excavation unearths the services leaving them intact without damaging them like shovels or excavators are prone to.

Vacuum Excavation to create small holes about the size of 300mm in diameter are considered potholes and may be undertaken to target a single service located by a service locator prior. Vacuum excavation that creates a larger strip or slot trench can be undertaken to expose many services in a cluster or to confirm there are no unknown services in a particular area of concern for future construction.

Potholing services is the highest level of accuracy for underground service location and is considered best practice for the recording & documentation of underground services.

Surveyors Role

It is preferable when undertaking service location and potholing to engage a surveyor for the accurate mapping (or as-builts) of any services identified or exposed. Service locators typically use spray paint or crayons to mark the results of the service location and these may disappear in a matter of days if they are marked on grass or if rain immediately follows the exercise. In relation to potholing it is not safe to leave exposed trenches open as they become a fall hazard for workers and the public so it is imperative to quickly have the surveyor locate & record the service prior to backfilling and reinstating the ground above the surface. The surveyor not only records the position and levels of the service, they also capture other attributes such as pipe materials, diameters that may be of benefit to designers.

Underground services that are located by a surveyor can be added to a Detail Survey plan that shows the positions and levels of the service along with reference data such as property boundaries and adjoining topographical features such as buildings, footpaths or kerbs. The data captured in the field is very data rich and it is not easy to create plots that contain all the features or attributes of the underground services, especially being able to differentiate when they may be captured via a mix of service locator, potholing or other methods. To clearly portray this information Bennett + Bennett adopt the Subsurface Utilities Standards (SUI) for conveying underground services on our survey plan deliverables.

Look out for Part 2 of this (3 Part series) on the ‘Capture & Recording of Underground Services – Australian Standards’ to be released next week. Part 3 to follow the week after.

If you have any questions on this topic then please contact Paul Cracroft-Wilson on 07 5631 8000 or mail@bennettandbennett.com.au