Foundation Excavations

Foundation excavations create the formation for strip footings, pad bases, raft foundations, and pile caps.
Depths vary from 600mm for shallow footings to several metres for deep pad bases and pile caps.
Trench collapse risk increases with depth, soft ground, surcharge loading, and proximity to existing structures.
Concrete is poured directly after excavation — workers must exit before the concrete delivery arrives.
Reinforcement fixing in foundation excavations requires safe access and protection from trench collapse.
Formation inspection by the engineer must confirm adequate bearing before concrete is placed.
Groundwater ingress into foundation excavations requires dewatering before workers enter safely.
Adjacent structures and roads impose surcharge loads that reduce the stability of excavation walls.
Spoil must be stored well back from the excavation edge to prevent overloading the sides.
Foundation excavations in contaminated ground require additional COSHH and environmental controls.

Burial risk	Trench collapse in foundation excavations buries workers under tonnes of soil, often fatally, within seconds.
Multiple hazards	Foundation work combines excavation, reinforcement, concrete, lifting, and groundwater hazards simultaneously.
Structural importance	Foundation formation must be correct — placing concrete on inadequate bearing ground causes building failure.

Do

Don't

Support or batter excavation sides for any foundation trench deeper than 1.2 metres
Inspect the excavation at the start of each shift and after rainfall before entry
Request the engineer to inspect the formation before concrete is placed
Dewater the excavation and confirm it is stable before workers enter
Keep spoil at least 1.5 metres from the excavation edge to prevent overloading
Provide safe access and egress using ladders or steps at regular intervals
Clear all workers from the excavation before concrete is discharged
Locate buried services before excavating, especially near existing buildings
Brief the team on the foundation layout, depths, and specific ground hazards
Apply COSHH controls where foundation excavations are in contaminated ground

DON'T enter an unsupported foundation trench deeper than 1.2 metres
DON'T allow workers to remain in the excavation during concrete pouring
DON'T place concrete on the formation before the engineer has inspected and approved it
DON'T stockpile spoil, materials, or plant close to the excavation edge
DON'T work in a waterlogged excavation without dewatering and stability assessment
DON'T ignore signs of ground instability such as cracking, bulging, or seepage
DON'T skip the daily excavation inspection even for shallow strip footings
DON'T dig adjacent to existing structures without assessing the impact on their foundations
DON'T excavate without checking for buried services along the foundation layout
DON'T fix reinforcement in deep excavations without safe access and trench support in place

See also: Excavation Safety Awareness | Trench Collapse Prevention

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