Incomplete or inadequate geotechnical information can be a major cause of project delays, cost blow-outs, and conflict. Here is some practical advice about how to reduce the risk of encountering one of the most common underground surprises.
The tender documents might tell you all you need to know about what needs to be built above the ground, but they may not have all the necessary information about the challenges lying underneath it.
Electronically Locate Services
On brownfield, infill or peri-urban sites, one of the major recurring issues is incomplete detail about the services including gas, stormwater, electrical, communications, sewerage and mains water pipework.
“The Information from DBYD is pretty good although it is only a guide,” Williams said.
In terms of the Australian Standards for utility detection, it is listed as a QL-D [Quality Level D] location level, which is “very much just indicative.” However, as Williams pointed out, “You need to electronically locate them and finally prove where they are as all services should be [surveyed] to a Quality Level A (QL-A).”
Williams has seen first-hand some of the DBYD accuracy issues. For instance, the utilities have been found on the opposite side of the road to where the information said they would be located.
What’s more, stormwater pipes are shown on less than 10 per cent of DBYD plans, as councils typically own them. In Sydney, for example, councils are not widely represented as DBYD asset owners. Also, the DBYD plans only show mains and do not include individual house connections for gas, water and private electrical connections.
Need Complete Picture of What’s Underground
In general, the information on subsurface risks is “not always as good as it should be, mainly due to cost and budgeting and clarity in what outcomes and deliverables they expect from the service locating company,” Williams explains.
He says nine out of 10 quotes that come into his company involve a degree of educating the client about what they actually need to get a complete picture.
Awarding service locating lowest bid may also be an issue as this can mean data collection may be compromised, Williams said.
Problems can also occur when the service locator is not marking to the Australian Standard, as the AS marking classifications ensure everyone involved knows how services have been located, which is key to knowing how accurate the survey is.
There are some red flags a builder should keep an eye out for. Quality B data, as defined by the Standard, means electromagnetic surveys only, not ground-penetrating radar. Meanwhile, DBYD mains surveys only will not account for stormwater, mains water, gas, electrical or sewer connections to houses or house lots.
Williams suggests building in contingencies for unexpected subsurface items by allowing time before starting work on site to get “the complete picture of what’s underground…instead of a false sense of duty of care by having a plan that is not complete.”
Have Safety Front of Mind
The proper identification process is a major safety issue, he explains. For instance, rupture of a gas main or electrical conduit poses an immediate risk to workers on site as well as a potential risk to the broader community. This opens the door for both potential legal complications and costly project delays.
“Work has to stop at that part of the site in case of an incident,” Williams says.
Where a project does have a subsurface utility detection specialist on-site, Williams says it is best to pay for a two-person crew as some scans require extra help or access to get the job done. Therefore, going with a sole operator could result in a fine-print disclaimer that the survey wasn’t fully completed.
The safety of workers is one of the major reasons accurate and comprehensive utility detection matters. “Our company helps workers stay safe. We do this by always locating to the best of our abilities with our scanning processes and experience.”
His team always has the “thought in the back of our mind to keep whoever is planning to dig up a trench, footing or footpath safe from damaging underground services.”
Doing it Right the First Time Saves Time and Money
The toolkit for investigations includes electromagnetic detection equipment and ground-penetrating radar. The team then marks the location of utilities using the Australian Standard marking system.
“To get accurate data collection, we pick up the markings with total station survey to within a few millimetres.”
Non-destructive vacuum excavation techniques are generally used for any potholing or trenching where utilities need to be exposed.
The company also provides drafting services in 2D or 3D where needed, and it can overlay findings onto existing survey plans or aerial imagery, such as satellite or drone images. Survey results can also be configured into files that can be integrated into a BIM model.
Williams says drones are becoming useful as part of the process, They’re used to survey for general signs of utilities, such as scarring from trenching or slumping of areas of the site over older trenching. Online maps and satellite imaging are also used to help identify signs of utilities before attending site.
Ultimately, doing due diligence in terms of accurately locating all subsurface utilities is a legislative requirement, Williams noted. Failing to do so will mean a builder can be liable for damages.
“Do it right the first time, and you save a big chunk of time and money and improve safety. You can save money upfront by skimping—but what price can you put on safety?”