EXC/Hazards/TBT-EXC-010

Trench Sheeting and Shoring

Excavations › Hazards › Trench Sheeting and Shoring

Presenter		Project
Location		Date

Trench sheeting and shoring prevent the sides of excavations from collapsing onto workers below.
Unsupported trench sides can collapse without warning, burying workers in seconds.
One cubic metre of soil weighs approximately 1.5 tonnes — enough to cause fatal crush injuries.
Support systems include timber shoring, hydraulic frames, trench sheets, and proprietary trench boxes.
The temporary works design must match the actual ground conditions and excavation depth on site.
A competent person must inspect the support system before each shift and after any event affecting stability.
Surcharge loads from plant, spoil heaps, and materials near the trench edge increase collapse risk.
Water ingress weakens trench sides and can cause sudden collapse even in stable soils.
The CDM Regulations 2015 and BS 6031 set requirements for safe excavation support design.
Removal of sheeting and shoring must follow a planned sequence, typically bottom-up as backfilling proceeds.

Prevent burial	Trench collapses kill and seriously injure construction workers every year in the UK. Most are preventable with proper support.
Legal requirement	CDM 2015 Schedule 2 requires excavations to be supported to prevent collapse and danger to any person.
Speed of collapse	Trench sides can fail in less than a second, giving workers no time to escape without support systems in place.
Changing conditions	Rain, vibration, surcharge loads, and drying all change soil strength, making ongoing inspection essential.

Don't

Install sheeting or shoring before anyone enters an unsupported trench.
Ensure the support system is designed for the actual ground conditions on site.
Inspect the support system before every shift and after heavy rain.
Keep spoil heaps, plant, and materials at least 1 metre from the trench edge.
Monitor for water ingress and arrange pumping before it weakens the sides.
Follow the temporary works procedure for installing and removing support systems.
Use a competent person to inspect excavations as required by CDM 2015.
Ensure safe access and egress is maintained within the supported trench.
Remove shoring in the correct sequence as backfilling progresses upward.
Stop work and evacuate if you see cracking, bulging, or water seepage in walls.

DON'T enter any unsupported trench deeper than 1.2 metres in any soil type.
DON'T place excavated spoil or heavy plant within 1 metre of the trench edge.
DON'T remove shoring panels out of sequence or before backfill reaches that level.
DON'T ignore cracks, bulging, or water seepage in the trench side walls.
DON'T assume the ground is stable because it looks firm on the surface.
DON'T use damaged or bent sheeting and shoring components in the trench.
DON'T allow vibrating plant to operate close to the trench without assessment.
DON'T skip inspections after overnight rain, frost, or adjacent plant movements.
DON'T alter the temporary works design without approval from the TWC.
DON'T work below unsupported overhangs or undercut trench walls.

See also: Trench Collapse Prevention | Excavation Inspection Requirements

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