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Excavation Work

What is Excavation Work?​

Excavation means removing soil or rock using tools, machinery or explosives to form open trenches, holes or cavities.

Common Construction Excavations:

  • Trenches for footings, services, drainage
  • Bulk excavation for basements, cut-and-fill
  • Service pits
  • Bored piles

When is Excavation High-Risk Construction Work?​

Excavation is HRCW requiring SWMS if:

  • Depth > 1.5 meters, OR
  • Risk of person falling in (any depth)

Major Hazards​

Collapse of Excavation Walls: Most serious risk - can bury and kill workers instantly.

Underground Services: Striking gas, electricity, water, telecommunications.

Falls into Excavation: Workers or public falling in.

Mobile Plant: Excavators, trucks reversing near excavation edge.

Asphyxiation/Toxic Atmosphere: Deep excavations may have oxygen deficiency or toxic gases.

Before Excavating - Service Location​

[!warning] Always Dial Before You Dig Striking underground services causes deaths, serious injuries, major disruptions. Service location is mandatory.

Process:

1. Dial Before You Dig (1100):

  • Call at least 2 business days before excavating
  • Obtain plans showing underground services
  • Free service

2. Locate Services on Ground:

  • Use plans and cable/pipe locators
  • Mark position with paint or pegs
  • Assume all services are live and pressurized

3. Hand Dig to Expose:

  • Within 500mm of marked services, hand dig only
  • Use spades/shovels (not picks or mattocks)
  • Carefully expose services
  • Confirm type, depth, condition

Underground essential services exposed by potholing Figure: Underground essential services exposed by potholing

4. Protect Exposed Services:

  • Support services crossing excavation
  • Protect from damage
  • Maintain clearances
  • Backfill properly when complete

Preventing Excavation Collapse​

Assessing Collapse Risk​

Factors Affecting Stability:

  • Soil type (clay more stable than sand)
  • Moisture content (wet soil less stable)
  • Depth
  • Nearby loads (plant, stockpiles, traffic)
  • Vibration
  • Previous excavation/disturbance

When is Shoring/Battering Required?

  • Always for excavations >1.5m in unstable soil
  • Any excavation where collapse risk exists
  • Competent person assesses stability

Control Measures​

Level 1: Elimination

  • Avoid excavation (alternative construction methods)
  • Trenchless technology (pipe bursting, boring)

Level 2: Engineering Controls

Battering (Sloping Walls):

  • Cut walls at safe angle (typically 1:1 or flatter)
  • Depends on soil type
  • Requires more space
  • Most reliable for short-duration work

Battering Figure: Battering - sloping walls

Shoring (Prevents Collapse):

  • Hydraulic/mechanical supports hold walls
  • Prevents collapse from occurring
  • Allows vertical walls (less space)
  • Must be designed by competent person
  • Installed progressively as excavation deepens
  • Removed carefully during backfilling

Hydraulic shoring Figure: Hydraulic shoring (soldier set style)

Shields and Boxes (Protects Workers):

  • Designed to protect workers if a collapse occurs
  • Does not prevent collapse of excavation walls
  • Only for worker safety, not ground support
  • Do not assume shield will hold up a wall

Trench shield Figure: Typical trench shield

Benching:

  • Step excavation in stable soil
  • Reduces wall height
  • May combine with battering

Benching Figure: Benching

Level 3: Administrative/PPE

  • Exclusion zones
  • Barricades/barriers
  • Warning signs
  • Competent supervision
  • SWMS
  • PPE (hard hats, boots, hi-vis)

Inspection​

Daily Inspection Required:

  • Check for cracks, subsidence
  • Check supports tight and secure
  • After rain, vibration, ground movement
  • By competent person

Safe Access and Egress​

Requirements:

  • Safe means of entry and exit
  • Ladder secured, extends 1m above excavation
  • Clear path to access point

Deep Excavations: Multiple access points may be needed.

Edge Protection​

Falls into Excavation:

  • Barriers approximately 1.5m from edge (prevents collapse and falls)
  • Guardrails if excavation remains open
  • Covers over narrow trenches (must support traffic loads)
  • Adequate lighting
  • Warning signs

Exclusion Zones: Keep plant and vehicles back from edge (minimum 1.5 times excavation depth).

Stockpiles and Spoil​

  • Minimum at least 1m (1000mm) from excavation edge (prevents surcharge loading)
  • Consider wall stability when placing
  • Do not undercut stockpiles

Excavated material and loads near excavations Figure: Excavated material and loads near excavations - Effect of zone of influence

Excavated material impact on effective excavation depth Figure: Placing material on lower side reduces effective depth

Confined Space Considerations​

Deep Excavations May Be Confined Spaces:

  • Limited entry/exit
  • Unfavorable atmosphere
  • Not designed for continuous occupancy

When Confined Space: Apply confined space requirements:

  • Atmospheric testing
  • Ventilation
  • Entry permits
  • Rescue procedures

Dewatering​

Water in Excavation:

  • Destabilizes walls
  • Slip/drowning hazard

Controls:

  • Pump out water
  • Cut off water source
  • May require engineered dewatering system
  • Monitor wall stability (water removal can cause collapse)

Practical Example​

Scenario: Excavating trench for sewer line (2m deep, 50m long)

Before Excavating:

  1. Dial Before You Dig - plans obtained
  2. Services marked (water main, electricity, telecommunications)
  3. Cable locator confirms positions
  4. Hand dig trial holes - services exposed and confirmed
  5. SWMS prepared

During Excavation:

  • Excavator maintains 500mm clearance from services
  • Hand dig close to services
  • Walls battered 1:1 (stable clay soil)
  • Ladder every 15m
  • Barriers 1.5m from edges
  • Daily inspections before work

Result: Excavation completed safely, no service strikes, no collapses.