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Excavation involves removing rock and soil from site to form an open face, hole or cavity. Trenches and shafts are high-risk excavations, so you’ll need to take extra precautions for managing the associated risks.
Typical jobs that require excavation are:
- Site cuts and preparation
- Under slab service installations for plumbing, electrical, gas and telecommunication services
- Waste and sewerage installations
- Pool construction
- Underground carpark and basement construction.
Planning and risk assessment
Common hazards related to excavation that require planning and risk assessment include:
- Falling into an excavation
- Being trapped in a collapsed excavation
- Being struck by a falling object such as earth or rock, while working in an excavation
- Being exposed to hazardous atmospheres and airborne contaminants within an excavation, such as carbon monoxide build-up from plant exhaust or PVC glue solvent (Methyl Ethyl Ketone) in poorly ventilated trenches
- Inrush of water or other liquids
- Underground and overhead services such as gas, water, sewerage, communications, electricity, chemicals and fuel or refrigerant lines
- Undermining adjacent structures
- Hazardous manual tasks
- Movement of mobile plant
- Environmental noise
- Working near excavating machinery and operating plant.
You should begin risk management for excavation work at the planning stage of the project.
Consult with the excavation contractor and plant operators to identify existing hazards, assess the risks and determine what control measures need to be implemented.
Excavation work is a high-risk construction activity, so you’ll need to prepare a Safe Work Method Statement before work begins.
If work is in proximity to existing structures, you may also need to consult geo-technical or structural engineers to ensure the structural integrity of the neighbouring structure.
Locating service lines
Before breaking ground, you’re legally required to locate any essential underground services and advise relevant stakeholders of the service line locations.
In the case of overhead power lines, if approach distances can’t be confirmed or work can’t be performed without maintaining minimum exclusion zones, you should contact the network owner, such as Energex or Ergon Energy, for advice.
You can also read about managing underground and overhead services.
Preventing ground collapse
Excavation can cause ground collapse due to:
- Wall instability
- Excess weight in the influence zone
- Incorrect controls supporting the sides of a trench.
Before excavating, it’s important to consider the ground conditions, review available geotechnical reports, decide how the spoil will be removed from site, and determine where plant and machinery will be required in and around the excavation.
Safeguard minimum 1.5 metre deep trenches from collapsing either by:
- Benching – involves stepped excavations of the trench wall
- Battering – involves sloped excavation of the trench wall to a maximum angle of 45 degrees
- Shoring – involves shielding, boxing or using engineered supports to prevent wall collapse.
Restrict unauthorised access
Restrict unauthorised access to trenches with a minimum depth of 1.5-metres. You can restrict access by securing the area with physical barriers, such as fencing, which protect workers from risk.
Mobile plant safety
There are risks involved with working in or around powered mobile plant or operating plant near the edge of an excavation.
Before excavation begins ensure:
- Correct plant is chosen for the task
- Plant operators are fully trained and competent
- There is a Safe Work Method Statement prepared
- Workers have been appropriately inducted
- Only relevant workers have access to the excavation zone.