Guide
Excavation and foundation safety
HSE requirements for safe excavation and foundation work on construction sites. Covers trench support systems, edge protection, safe access, cable and pipe avoidance, inspection duties, and emergency procedures for collapse. Trench collapse is a leading cause of construction fatalities in the UK.
Trench collapse is one of the leading causes of death on UK construction sites. Excavations can collapse without warning, even in apparently stable ground. Every year, workers are killed or seriously injured because excavations were not properly supported, inspected, or managed.
If you carry out excavation or foundation work, you have legal duties under the Construction (Design and Management) Regulations 2015 (CDM 2015) to prevent collapse and protect everyone working in or near the excavation. These duties apply regardless of depth. Even shallow trenches can collapse and bury a worker.
Excavation work is classified as work involving particular risks under CDM 2015 Schedule 3 (item 1: risk of burial under earthfalls). The construction phase plan must include specific measures to address excavation risks, and a competent person must supervise all excavation work.
Before you start: planning and preparation
Most collapses happen because the work was not planned properly, ground conditions were not assessed, or underground services were not located before digging began. Complete these steps before any excavation work starts:
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1. Appoint a competent person to supervise
A competent person must supervise all excavation work. They must have sufficient training, experience, and knowledge to decide what support is needed, identify hazards, and determine safe working methods. They must be on site whenever excavation work takes place.
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2. Assess ground conditions and plan support
Assess soil type (clay, sand, gravel, rock, made ground), moisture content, water table level, and proximity to structures, roads, or railways. The competent person must decide what support system is needed. No excavation should proceed without a clear plan for preventing collapse.
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3. Locate all underground services
Obtain plans from all utility asset owners via LSBUD (LinesearchbeforeUdig). Scan the full excavation area with a cable avoidance tool (CAT) and signal generator (Genny). Mark located services on the ground. Plans show approximate routes only and cannot be relied upon for exact positions.
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4. Prepare a method statement
Cover the excavation sequence, support system, edge protection, safe access and egress points, underground services precautions, materials storage setback distances, vehicle controls, and emergency procedures. For notifiable projects, include these in the construction phase plan.
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5. Set up emergency rescue arrangements
An emergency plan covering rescue from collapse, flooding, and utility strikes must be in place before work begins. Rescue equipment (harnesses, ropes, breathing apparatus where confined space conditions may exist) must be available at the excavation site.
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6. Brief all workers
Every person working in or near the excavation must receive a site-specific briefing on underground service locations, support arrangements, edge protection, safe access points, exclusion zones, and emergency procedures.
Supporting the excavation and protecting the edges
The competent person must decide what support system is appropriate before work begins. The choice depends on ground conditions, depth, width, and duration of the excavation, plus any nearby structures or vehicle loads affecting stability. Support must be installed as the excavation progresses. Workers must never work in an unsupported excavation where there is any risk of collapse.
Edge protection and access
Guard rails and toe boards must be provided at the edges of all excavations where anyone could fall in. Guard rails must be a minimum of 950mm above ground level. Do not rely on spoil heaps or hazard tape.
Provide ladders or steps for safe entry and exit. Ladders must extend at least 1 metre above the landing point. Position access points so no worker is more than 25 metres from a means of escape.
Materials and vehicles near excavations
Keep excavated material, plant, and heavy loads well back from the edge. The minimum setback distance should equal the depth of the excavation. Install stop blocks or barriers to prevent vehicles driving into or overloading the edges. Use a banksman where vehicles operate near open excavations.
Locating and avoiding underground services
Striking an underground electricity cable or gas pipe during excavation can be fatal. HSE guidance HSG47 sets out the safe digging practices you must follow.
Cable avoidance tools indicate the approximate line of a service but do not reliably indicate depth. The critical rule is: hand dig within 500mm either side of any located service. No mechanical excavation is permitted within this zone. When crossing a service at an angle, hand dig to expose it before using mechanical plant. Use insulated hand tools where electrical cables may be present, and never use picks or pointed tools directly above buried services.
Inspections during excavation work
CDM 2015 Regulation 22 requires a competent person to inspect excavations:
- Before each shift - before any worker enters at the start of every shift
- After heavy rain or flooding - water weakens trench sides
- After vibration from nearby plant - piling, compaction, or heavy vehicles can destabilise walls
- After accidental disturbance - including vehicle loading near the edge
- After unexpected conditions - voids, running sand, water ingress, or uncharted services
The competent person must prepare a written inspection report after each inspection. Reports must be kept on site until the work is complete, then retained for 3 months. HSE inspectors will ask to see these records.
Emergencies, utility strikes, and RIDDOR reporting
Excavation collapse
If an excavation collapses or shows signs of instability (cracking, bulging, movement of supports), evacuate immediately. If anyone is trapped, initiate the rescue plan and call 999. Do not attempt an unplanned rescue by entering the collapsed excavation without proper equipment and trained personnel.
Utility strikes
If you strike an electricity cable, do not touch the cable or equipment in contact with it. Warn others to stay clear and call the distribution network operator. If in a machine cab, stay in the cab unless there is a fire risk; if leaving, jump clear with both feet together.
If you strike a gas pipe, evacuate the area, eliminate all ignition sources, and call the National Gas Emergency Service on 0800 111 999.
RIDDOR reporting for excavation incidents
Certain incidents must be reported under RIDDOR 2013:
- Collapse or partial collapse of an excavation is a dangerous occurrence reportable within 10 days, even if no one was injured
- Burial or trapping by collapse is a specified injury reportable immediately by telephone (0345 300 9923), followed by online report within 10 days
- Utility strikes on gas or electricity are dangerous occurrences reportable within 10 days
Failure to report is a criminal offence carrying an unlimited fine.
What to do next
If you are planning excavation or foundation work:
- Check your competent person arrangements - confirm a suitably qualified person will supervise every excavation
- Review your emergency rescue plan - ensure rescue equipment is available and workers are trained
- Order utility searches - contact LSBUD to identify asset owners and request plans well in advance
- Check your construction phase plan - ensure excavation risks are addressed as CDM Schedule 3 particular risks
- Set up your inspection regime - prepare for pre-shift inspections and written reports
For related guidance, see: