The Collapse Risk
Excavation collapses happen quickly and without warning. One cubic metre of soil weighs approximately 1.5 tonnes—enough to crush and suffocate anyone trapped beneath it. Even shallow trenches can kill; there is no safe depth at which precautions become unnecessary.
Add the risk of striking underground utilities—causing electrocution, explosions, or flooding—and excavation work demands rigorous planning and control.
Legal Requirements
CDM 2015
Excavation work must be planned, managed, and monitored to ensure safety. Specific requirements include:
- Suitable and sufficient support or battering to prevent collapse
- Prevention of falls into excavations
- Prevention of materials falling onto workers
- Underground services identified and precautions taken
Inspections
Excavations must be inspected by a competent person:
- At the start of each shift before work begins
- After any event likely to affect stability
- After any accidental fall of materials
Written reports are required, kept on site until work is complete.
Underground Services
The "Safe Digging" Process
- Plan: Get utility records, identify what's expected
- Detect: Use cable locators and ground penetrating radar
- Confirm: Hand dig trial holes to expose services
- Excavate: Use safe digging practices
Utility Records
- Contact all utility owners—not just the obvious ones
- Electricity, gas, water, telecoms, drainage, traffic signals
- Use LinesearchbeforeUdig for statutory utilities
- Check with site owner for private services
- Mark locations on ground using HSE colour codes
Cable Locating
- Use combined CAT and genny (signal generator)
- Scan in power mode, then radio mode, then genny mode
- Operators must be trained and competent
- Understand limitations—some services won't be detected
- Treat all unidentified signals as live services
Safe Digging Practices
- Hand dig within 500mm of known services
- Use insulated tools when digging near electricity
- No mechanical excavation over or near services without precautions
- Treat all cables as live until proven dead
- Support exposed services immediately
- Report any damage immediately—don't try to repair
Preventing Collapse
Factors Affecting Stability
- Soil type (clay, sand, gravel, made ground)
- Water content and groundwater
- Depth and width of excavation
- Adjacent structures and surcharges
- Vibration from traffic or machinery
- Weather conditions
- Time the excavation is open
Methods of Support
Battering (Sloping)
Cutting the sides at a safe angle. Requirements:
- Angle depends on soil type (typically 45 degrees or less)
- Requires significant space
- Must be designed by competent person for deeper excavations
Shoring
Supporting the sides with props and boards:
- Trench sheets or timber sheeting
- Hydraulic or mechanical props
- Must be installed progressively as excavation deepens
- Must be designed by competent person
Trench Boxes
Pre-fabricated support systems:
- Lowered into excavation as work progresses
- Rated for depth—don't exceed
- Must extend above ground level
- Workers must stay within protected area
When is Support Required?
There is no "safe" depth. Consider support for any excavation where workers might be buried or struck by falling material. In practice:
- Trenches over 1.2m deep typically require support or battering
- Shallower excavations may need support depending on soil and conditions
- Any excavation where workers might be trapped needs consideration
Preventing Falls Into Excavations
- Guard rails along edges (950mm high minimum)
- Barriers to prevent vehicles approaching
- Covering excavations when unattended
- Adequate lighting if work continues after dark
- Safe access points (ladders, steps)
- Keep the area clear of trip hazards
Other Excavation Hazards
Falling Materials
- Keep spoil and materials back from edge (minimum 1m)
- Don't store materials where they could fall in
- Protect workers from collapse of trench sides
- Head protection for workers in excavation
Water Accumulation
- Assess groundwater conditions before digging
- Plan for dewatering if needed
- Monitor water levels
- Pumping equipment must be suitable and maintained
Contaminated Ground
- Assess site history for contamination risk
- Test soil if contamination suspected
- Appropriate PPE and controls
- Proper disposal of contaminated material
Confined Spaces
Deep or enclosed excavations may become confined spaces with atmospheric hazards. Apply confined space procedures where:
- Natural ventilation may be inadequate
- Contaminated ground may release gases
- Services may leak
- Work processes generate fumes
Excavation Risk Assessment Checklist
- Underground services identified and located?
- Soil conditions assessed?
- Groundwater conditions known?
- Adjacent structures assessed for impact?
- Support or battering requirements determined?
- Support designed by competent person?
- Edge protection planned?
- Safe access designed?
- Inspection regime established?
- Emergency procedures in place?
- Atmospheric hazards considered?
- Welfare facilities adequate?
Competence Requirements
- Excavation design: Competent engineer for deeper/complex excavations
- Inspection: Training and experience in excavation hazards
- Cable avoidance: Trained CAT/genny operators
- Machine operators: Appropriate plant certification
- All workers: Briefed on specific hazards and controls
Conclusion
Excavation work is high-risk but manageable with proper planning. The key is treating every excavation seriously—assessing ground conditions, supporting the excavation appropriately, protecting workers from falls, and never taking shortcuts with utility location.
When generating RAMS with DocGen, include details of the excavation depth, ground conditions, and services present. The AI will identify common excavation hazards, but site-specific assessment by a competent person remains essential.