Excavation and foundation safety

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:

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. As industry good practice, 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 event-triggered inspections. For routine start-of-shift inspections, CDM 2015 regulation 24(4) requires no more than one written report in any 7-day period. 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

Excavation incidents are reportable under RIDDOR 2013 where they meet the Schedule 2 or regulation 4 criteria:

• Collapse - the unintentional collapse of a structure or falsework, or a collapse involving more than 5 tonnes of material in construction work, is a dangerous occurrence reportable within 10 days. A trench collapse with no injury is not automatically reportable unless it meets one of these descriptions
• Injuries from burial - loss of consciousness caused by asphyxia, or hypothermia or heat-induced illness requiring resuscitation or admission to hospital for more than 24 hours, are specified injuries reportable without delay by telephone (0345 300 9923), followed by an online report within 10 days. Burial without injury is not itself reportable
• Utility strikes are reportable as dangerous occurrences only where a Schedule 2 item is met - for example an electrical short circuit or overload causing fire or explosion that stops plant for over 24 hours or creates significant risk of death, or an accidental release of 10 kg or more of flammable gas. A typical service strike with no fire or explosion is not reportable

Failure to report a reportable incident 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:

• CDM 2015: your duties as a construction client
• Construction site health and safety