Excavation for foundations: risk assessment and method statement
Excavating foundation trenches at the site with an excavator to the depths and widths on the engineer's drawings, with spoil managed, trenches inspected and access controlled.
Risk assessment
Risk = severity × likelihood, each from 1 to 5. 1 to 3 is low, 4 to 6 medium, 8 to 12 high and 15 to 25 very high.
| Hazard | Who might be harmed and how | Risk | Controls | With controls |
|---|---|---|---|---|
| Collapse of trench sides | Operatives entering the trench may be buried by collapsing sides, causing crush injury or death. | 5 × 3 = 15 Very high |
| 5 × 1 = 5 Medium |
| Striking buried services | Operatives may strike live cables or gas pipes while digging. | 5 × 3 = 15 Very high |
| 5 × 1 = 5 Medium |
| Struck by the excavator | Operatives may be struck by the bucket or body of the excavator. | 5 × 2 = 10 High |
| 5 × 1 = 5 Medium |
| Falls into open trenches | Operatives and others may fall into open trenches, causing fractures or head injury. | 4 × 3 = 12 High |
| 4 × 1 = 4 Medium |
| Plant and vehicles near trench edges | Plant or vehicles may overturn into the trench or cause the sides to collapse. | 5 × 2 = 10 High |
| 5 × 1 = 5 Medium |
| Undermining adjacent structures | Neighbouring walls, footings or boundaries may be undermined and collapse. | 4 × 2 = 8 High |
| 4 × 1 = 4 Medium |
| Water ingress and flooding | Operatives may be at risk if water floods the trench or softens the sides. | 3 × 3 = 9 High |
| 3 × 1 = 3 Low |
| Access and egress | Operatives may fall or be trapped without safe access into and out of the trench. | 3 × 2 = 6 Medium |
| 3 × 1 = 3 Low |
| Contaminated ground | Operatives may be exposed to contaminated soil or ground gases. | 3 × 2 = 6 Medium |
| 3 × 1 = 3 Low |
Weather: Stop in heavy rain, flooding or frost; re-inspect trenches after rain before entry.
Method statement
Supervision and briefing
Operations will be controlled by a competent supervisor.
All operatives involved will be briefed on:
- Trench support and inspection requirements
- Buried services and scan results
- Plant exclusion zones
- Emergency procedures including trench rescue
PPE
- Safety boots
- Gloves
- Hi-visibility clothing
- Hard hats
- Eye protection where necessary
Plant and equipment
- Excavator with certificated operator
- CAT and Genny
- Trench support (boxes or sheets) where required
- Barriers and stop blocks
- Ladders for access
- First aid kit
Things to watch for
Excavations at the site may be close to boundaries, existing buildings and buried services.
Particular care must be taken to avoid:
• Trench collapse
• Buried services
• Undermining neighbouring structures
The engineer's foundation drawings will be followed and any change agreed in writing.
Working conditions
Trenches will be barriered at all times. Spoil will be kept back from edges. Trenches will be inspected at the start of every shift.
Access
Access to the work area is via the the site grounds. Spoil will be removed by dumper to the agreed stockpile or muck-away lorry.
Where the work is
Foundation trenches at the site as set out from the engineer's drawings.
Sequence of work
- Brief operatives on trench safety, services and exclusion zones.
- Check setting out, service plans and scan the area.
- Hand dig trial holes at indicated services.
- Set up barriers and plant exclusion zones.
- Excavate trenches to the required depth and width.
- Support or batter trenches before anyone enters.
- Inspect trenches before entry and at the start of each shift.
- Keep spoil at least 1m back from edges.
- Arrange Building Control inspection of the formation.
- Barrier or cover trenches at the end of each day.
Emergencies
Stop work immediately, make the area safe, move people out of danger, report it to the site manager or supervisor, and call 999 if anyone is hurt or in danger.
References
CDM 2015 reg 22 (excavations); HSE HSG47 Avoiding danger from underground services; HSE HSG150