Non-destructive Vacuum Excavation

Non-destructive Excavation and Underground Service Potholing

What is the advantage of knowing exactly where the underground services are before you commence construction and building works? It might be as clear as mud but having accurate information at your work site could be the difference meeting making your safety targets or getting over the hump of crossing a critical high pressure or high voltage service.
Some of the advantages are:
  • Planning construction around the exact depths and position of the service
  • Heights of proposed services can be designed precisely
  • Safety to workers and community by avoiding service disruptions
  • Knowing how many or what type of services are below

Ready to Call Geoscope first.

How do you find out the exact location of buried services?

There is finding services using utility detection equipment which will always have room for tolerance and then there’s knowing the exact location by actually seeing the service with your own eyes. This process is commonly referred to as Potholing.
Potholing a service can be done in various ways such as:
  • Hand digging or hand excavation
  • Non-destructive digging
  • Non-destructive excavation
  • Hydro-excavation
  • Vacuum excavation
  • Air-vacuum excavation

How does Non-destructive Excavation work?

The typical process for Non-destructive excavation (NDE) around utilities starts with identifying what services are below you work site using DBYD plans, existing survey plans and electronic locating methods.

Once the underground services have been located using our electronic locators and radars, we can pin point the locations by digging down with high pressure water to dislodge and loosen the soil without the need of mechanical machinery, which has a high risk of potential damages or breaks.

As the soil breaks away from the high water pressure being fired at the target pothole location, it gets lifted through a hose by negative pressure generated by the truck mounted vacuum tank. Also known as a sucker truck, it’s like creating a mud thick shake with the dirt and sucking it through a very large, industrial straw.

As the soil, slurry is being removed, and the pothole is getting deeper, we’re getting closer to exposing the pipe or cable needing to be positively identified. As we get closer to the service, we don’t need to back off at all, we dig as hard as we can with the water under recommended safe high-pressure water jet to allow risk-free disruption or damage to the asset.

Removing the risk or hazard of damaging the underground services is the main focus of any building work-site and using Geoscope to safely identify these services is the safest way.

Recording the actual depths and locations of underground services

Now that the services at your site have been safely exposed and identified, it makes sense to record the findings on a plan or through photo reporting. The Australian Standard – Classification of Subsurface Utility Information classes a potholed or exposed service, which has been measured in 3-dimension and the utility diameter, material etc is all recorded to be a QL-A or a Quality Location Level A.

By having all the information and depths of potholed services at hand on your work site, you will:
  • Fulfil your duty of care when working around critical services
  • Have permanent record and evidence of the findings
  • Be able to put plans in place to protect the services with future mechanical services
  • Avoid expensive repairs and damages

The look of relief on our clients face when we expose the underground services safely makes it all worthwhile! Like somehow, they are shock and surprised that our pipe and cable detection methods were some sort of science fiction.

But exposing underground services is all part of the process in gathering the subsurface utility information set out in the Australian Standards.

By getting an accurate and positive identification on a utility means we can precisely record the depths and location in 3-dimensional space.

Not only can we see the pipe or conduits, but we are at a greater advantage to minimise any further risks in damaging them by implementing a safe work procedure around it.

And that’s what it is all about.
  • Planning what disruptive tasks to be undertaken
  • Locate what’s in the work area with electronic locating devices
  • Map the findings with a utility survey
  • Pothole and verify the electronic readings
  • Protect the existing underground utilities
  • Proceed with your works safely and efficiently

Should I have potholing done on my project?

If you have critical services on your site such as fibre optic cables owned by Telstra and Optus or High-pressure gas pipes managed by Jemena and APA group or Freyssinet or HV electricity cables, these services at a minimum need to be identified prior to excavating in the vicinity or crossing the actual service.

If you would like to expedite the excavation process around congested services without rushing the mechanical excavation stage and putting risk to the project by a potential partial site flooding from a ruptured water pipe, then potholing is definitely recommended.

If all you are looking to do is fulfil your duty of care when working around underground services and in turn, complete your obligations to your public liability insurance, then you guessed it! You really should have potholing completed on your project.

These critical services can have minimum approach distances ranging from 2 metres to 30 metres.

This means if you have a critical service at your work site, you’ll basically need to put some steps in place to avoid damaging and causing, all which have been mentioned above.

What happens to the soil that is removed from potholing?

Once the soil and water mixture is sucked into the vacuum tank, it will now need to be disposed of appropriately. The slurry is now contained air tight in the vac trucks spoil tank and is commonly transported to EPA certified tipping facilities to be tipped.

These facilities are often outside of the city CBD so consideration must be taken for the time to take the waste away and return to site or the depot at the end of the day. The water and soils can be separated and recycled making this method not only environmentally safe but saves any issues from potential fines from incorrect disposal.

Some problems faced with tipping at these sites is they don’t allow you to tip contaminated or hazardous soils such as asbestos, hydro carbons or sulphate soils etc.

Issues with potentially contaminated soils uncovered when using NDD to expose asbestos cement (AC) or soils with sulphates etc means these particles have now been mixed through the vacuum tank and the whole load is contaminated. Telstra conduits or other assets which contain fibrous material that can be found in underground pit and pipe work in various assets can be very harmful to the respiratory system.

That is why the correct procedures must be followed identify the potential contaminated soils but also to tip this waste slurry appropriately.

Quite common on larger projects, having a soil test on site from environmental geologist to determine soil properties in fill, natural, rock and water tables are undertaken well before a project requiring earthworks or building begins. Once the builder has the paperwork saying the land to be potholed with non-destructive excavation does or does not have any contaminants, we can plan our transportation routes accordingly to fulfil our duty of care.

Can high pressure water damage underground utilities when potholing?

Short answer, anything is possible. In reality, we use water pressure up to 2000 psi which is enough to break through the hardest soils but safe enough to not puncture or damage any special coatings.

If you were to sit the high-pressure water stream in one localised spot for a extended period of time, then sure, some wear may be present on the underground service, although our job is to expose the service, not give it a spit polish to shine it up. Once we’ve opened the hole up and found what we’ve intended to find, we record the findings and move on. There’s simply no need or benefit to apply concentrated high-pressure water to a fixed point for an extend period of time.

Eliminate the risk

We often hear in safety inductions and toolbox meetings that if there is a safer way to do things, than we should be doing it.

There’s a little thing the hierarchy of control. We need an order of things we need to put in place to stay safe when working in high risk situations and some things are prioritised of other control measures.

Things like PPE – personal protective equipment is rated the lowest control measure someone should use to keep themselves safe on the job and things like mechanical barriers and lifting platforms are preferred.

The risk when excavating near live underground utilities is so great that one slip up can be deadly. When we identify an underground service as a risk, the control measure should be to pothole, identify and record the findings at appropriate intervals to the works being performed.

Once the service has been identified, the risk of striking the pipe or cable is greatly reduced if not eliminated completely.

If you are planning any sort of excavation work around buried services, call us to find out if we can help you locate and identify the services to greatly improve efficiency and safety on your next project.

Call before you dig