Trench collapses are sudden, violent, and frequently fatal. Unsupported trench walls can fail without warning, burying workers under tonnes of soil in seconds. The risk increases significantly with depth, poor ground conditions, nearby vibration sources, and water ingress. Proper support systems must be in place before anyone enters a trench, regardless of how quickly the task is expected to take.
Key Hazards
Sudden trench wall collapse burying operatives under heavy soil
Vibration from nearby plant destabilising unsupported trench sides
Water ingress weakening soil structure and causing sudden slumps
Surcharge loads from spoil heaps or plant too close to edges
Control Measures
Install trench support systems such as shoring, trench boxes, or sheet piles before any entry.
Ensure a competent person designs the support system based on ground conditions and trench depth.
Keep all spoil heaps, materials, and plant at least one metre from the edge of the trench.
Inspect trench conditions at the start of every shift and after any rainfall or vibration event.
Use battered slopes at safe angles where support systems are not practical for the ground type.
Dewater the trench if groundwater is present and monitor water levels throughout the works.
Restrict plant movement near trench edges and use stop blocks to prevent overrun.
Provide safe access and egress with ladders positioned within one metre of any work position.
Brief all operatives on the trench support plan and the signs of imminent collapse.
Emergency / Rescue
If a trench shows signs of movement or cracking, evacuate immediately. If someone is buried, call 999 and do not enter the trench. Remove spoil only if safe to do so without entering the excavation.
Remember
One cubic metre of soil can weigh over 1.5 tonnes — enough to kill in seconds.
Never enter an unsupported trench even for a task lasting only a few minutes.
Ground conditions can change rapidly after rain, frost, or vibration from nearby plant.
Cracks in the ground surface near a trench edge are a warning sign of imminent collapse.
The competent person must inspect the trench daily and after any significant change in conditions.
Applicable Legislation: CDM Regulations 2015 · Health and Safety at Work etc. Act 1974 · BS 6031 (Code of Practice for Earthworks)