Safe digging – six things landscapers need to know

From planting trees and installing fence posts to excavating for drainage and retaining walls, digging is part of everyday landscaping work. But what lies beneath the surface, and around the excavation, can pose serious risks. Here are six things to consider before breaking ground.

A spade through a buried electrical cable, an excavator bucket striking a gas main or a trench collapsing around a worker – excavation work can have serious consequences when the risks aren't properly managed.

For landscapers, those risks aren't limited to major earthworks. Even relatively shallow excavations for planting, irrigation, drainage or fence foundations can damage underground services, undermine nearby structures or expose workers to unstable ground.

WorkSafe New Zealand's Excavation Safety good practice guidelines outline precautions businesses should take before and during excavation work.

1. Know what's underground

Before breaking ground, establish whether underground services are present and where they're located.

These may include electricity cables, gas pipes, water and wastewater networks, telecommunications cables and private services connecting buildings to public infrastructure.

A useful starting point is beforeudig, New Zealand's underground asset information service, which allows contractors to request plans and information from participating utility asset owners.

However, not all asset owners participate, and plans may not show private services. Contractors may need to contact other service owners directly.

WorkSafe also warns that drawings may not accurately reflect what's underground. Infrastructure may have been installed differently from the original plans, moved during subsequent work or buried at depths that have changed over time.

Where services could be affected, appropriate locating equipment should be used to trace and mark their position.

Their exact location and depth may then need to be confirmed through careful excavation, commonly known as potholing, before mechanical excavation takes place nearby.

Hand digging isn't automatically safe. WorkSafe warns against thrusting tools into the ground or using metal picks, bars and similar equipment close to live electrical cables.

Vacuum excavation may be appropriate in some circumstances, subject to asset-owner requirements and an assessment of the risks.

Importantly, a beforeudig plan is not permission to excavate without further precautions. Asset owners may specify minimum approach distances, permits, excavation methods or supervision requirements.

2. Check overhead hazards

Underground services aren't the only infrastructure that can be damaged during excavation.

Excavators operating in residential gardens or along roadsides may come close to overhead power lines, power poles and their supporting wires.

Operators need to consider the machine's full operating reach, including its boom and attachments, rather than simply the position of its tracks.

WorkSafe identifies minimum approach distances for working near different types of infrastructure. These vary according to the service and circumstances, and closer work may require documented consent or a permit from the asset owner.

Before operating machinery, establish what overhead hazards are present and what restrictions apply.

3. Assess ground stability

Ground collapse is one of the most serious excavation hazards and WorkSafe warns that even trenches less than 1.5m deep can collapse and cause serious injuries.

This is particularly relevant to landscapers installing drainage, constructing retaining walls or excavating beside existing buildings.

Ground stability depends on several factors, including soil type, moisture content, excavation depth, nearby structures and additional loads.

Heavy rain can weaken soil, while machinery, stockpiled materials and vibration near excavation edges can increase the risk of collapse.

WorkSafe identifies several approaches to managing these risks:

• Benching and battering: stepping or sloping excavation sides to improve stability.

• Shoring: installing supports to prevent excavation walls collapsing.

• Shielding: using protective systems to protect workers if surrounding ground collapses.

  
  

The appropriate method depends on site conditions and should be determined with input from a competent person.

Remember that 1.5m is not a safe-depth threshold. Shallower excavations may also require protection where collapse is possible.

Excavations should be inspected before work begins each day and following events that could affect stability, such as heavy rainfall.

4. Protect surrounding structures

Excavation can also affect structures beyond the immediate work area.

Digging for retaining walls, pools or drainage may remove support from nearby building foundations, driveways, boundary walls or neighbouring properties.

Before starting, consider what the surrounding ground currently supports and whether excavation could undermine it.

Where stability is uncertain, competent assessment and, where necessary, geotechnical or structural engineering advice should inform the excavation method and any temporary support required.

5. Keep people away from danger

Safe excavation means managing what happens around the hole as well as inside it.

WorkSafe recommends keeping excavated soil, equipment and other loads sufficiently clear of excavation edges to avoid placing additional pressure on surrounding ground.

Workers need safe access into and out of excavations, while suitable barriers should prevent people or materials falling in.

Machinery presents additional risks. Even compact excavators have blind spots and can crush workers against walls, fences or other structures.

Exclusion zones should separate people from operating machinery wherever practicable. Where separation isn't possible, additional controls may include spotters and effective communication.

This is particularly important on residential sites where homeowners, children, visitors or other contractors may be nearby.

Excavations also need to be appropriately secured when work stops or the crew leaves the site.

6. Prepare for the unexpected

Under the Health and Safety at Work Act 2015, landscaping businesses must manage risks to workers and others affected by their activities, so far as is reasonably practicable. That includes planning for what happens if something goes wrong.

Before excavation starts, workers should know how to respond to a service strike, ground collapse or other identified emergency, including how to raise the alarm and prevent others entering danger.

Underground services should be treated as live or in use unless the asset owner confirms otherwise.

If an unexpected pipe or cable is discovered, work should stop until it has been identified and the risks reassessed.

For landscapers, the practical message is straightforward – obtain service information, confirm what's actually on site, assess ground and surrounding conditions, and establish appropriate controls before digging.

A little more preparation can prevent serious injury, costly infrastructure damage and significant project delays.