How to Write a RAMS for Excavation and Trenching: UK Guide

Why Excavation Work is High Risk

Excavation and trenching work is one of the most dangerous activities on any construction site. Trench collapse can happen without warning, and when it does, there is almost no time to react. A single cubic metre of soil weighs between 1.5 and 2 tonnes. Workers caught in a collapse face crush injuries, asphyxiation, or death within minutes.

Several factors increase the likelihood of collapse:

• Wet or waterlogged ground reduces soil cohesion

• Vibration from nearby plant, traffic, or piling work destabilises trench walls
• Surcharge loads (spoil heaps, materials, or vehicles stored too close to the edge)
• Previously disturbed or backfilled ground that has not consolidated
• Granular soils (sand, gravel) that have no natural cohesion

Even shallow trenches kill. The HSE has investigated fatal collapses in trenches less than 1.5m deep. Depth alone is not a reliable indicator of risk. Ground conditions, weather, and nearby activity all matter.

Legal Requirements

Excavation work on construction projects falls under the Construction (Design and Management) Regulations 2015 (CDM 2015). Schedule 3 of CDM specifically addresses excavations and requires that:

• Suitable and sufficient steps are taken to prevent danger from collapse, falling materials, or people falling into excavations
• Excavations are inspected by a competent person before any person carries out work at the start of every shift
• Inspections are also carried out after any event likely to have affected the strength or stability of the excavation (heavy rain, ground movement, accidental disturbance, nearby blasting)
• Results of inspections are recorded in writing and kept available on site

Beyond CDM, the Management of Health and Safety at Work Regulations 1999 require a suitable and sufficient risk assessment for all work activities. For excavation work, this means a RAMS that specifically addresses the ground conditions, support systems, access arrangements, and emergency procedures for that particular site and task.

Service Avoidance

Before any mechanical excavation begins, you must establish what is in the ground. Striking an underground service can cause explosions (gas), electrocution (power cables), flooding (water mains), or loss of critical infrastructure (fibre optic and telecoms).

Your RAMS must include a service avoidance procedure. The minimum standard is:

1. Obtain utility plans from all asset owners before work starts. Use a utility search provider to get up-to-date records for gas, electric, water, telecoms, and drainage.
2. Scan the ground with a CAT (Cable Avoidance Tool) and Genny (Signal Generator) across the full excavation area. The operator must be trained and competent in the use of the equipment. Scan in multiple directions.
3. Hand dig within 500mm of any known or suspected service. No mechanical excavation is permitted within this zone. Use insulated hand tools, not picks or forks.
4. Mark the location of identified services with paint or marker stakes before excavation begins.

HSE guidance document HSG47 (Avoiding danger from underground services) is the primary reference. Your RAMS should cite it and your operatives should be familiar with its requirements.

The golden rule: assume every trench has services until proven otherwise.

Key Hazards to Address in Your RAMS

Your excavation RAMS should address all of the following hazards as a minimum:

• Collapse and burial of trench walls onto workers in the excavation
• Striking underground services including gas mains, live electrical cables, water mains, and fibre optic lines
• Falls into the excavation by workers, members of the public, or vehicles
• Flooding and water ingress from groundwater, burst services, or surface water runoff
• Undermining adjacent structures including building foundations, retaining walls, boundary walls, and roads
• Plant operating near edges causing surcharge loading or vibration that destabilises the excavation
• Confined space conditions in deep excavations where gas accumulation or oxygen depletion is possible
• Manual handling of trench support equipment, shoring timbers, and heavy materials

Control Measures

Shoring and Support Systems

Any trench where there is a risk of collapse must be supported. The type of support depends on the depth, ground conditions, and duration of the work:

• Timber shoring uses walings, struts, and poling boards to hold back trench sides. Suitable for shorter duration works in reasonably stable ground.
• Hydraulic shoring (drag boxes or frames) can be installed from the surface without anyone entering the unsupported trench. This is the preferred method for most utility trenching.
• Trench boxes (shield systems) provide a protected working area within the trench. Workers remain inside the box at all times. Boxes are rated to specific depths and soil types.

Shoring must be installed progressively as the trench deepens and must not be removed until all work in that section is complete. The design of temporary support must be carried out or verified by a competent person.

Benching and Battering

Where space allows, trench sides can be cut back (battered) to a safe angle rather than using mechanical support. The safe angle depends on the soil type:

• Granular soil (sand, gravel): maximum 1:1 slope (45 degrees) as a general guide, though loose granular soils may require flatter angles
• Cohesive soil (clay): steeper angles may be possible in the short term, but clay dries and cracks, so monitor constantly
• Mixed or made ground: treat as the weakest soil type present

Benching (cutting steps into the trench side) is an alternative approach for wider excavations. Both methods require significantly more space than shoring and may not be practical in confined urban sites.

Edge Protection

Preventing people and vehicles from falling into the excavation is just as critical as preventing collapse:

• Install physical barriers (guardrails, fencing, or proprietary trench edge protection) set back at least 1m from the edge of the excavation
• Use stop blocks or bunds to prevent plant and vehicles from approaching the edge
• Provide adequate lighting for any excavation that remains open after dark
• Keep spoil heaps, materials, and equipment at least 1m from the trench edge to reduce surcharge loading

Access and Egress

Workers in trenches need a safe way in and out that does not require climbing the trench walls:

• Provide a ladder at intervals of no more than 15m along the trench length
• Ladders must extend at least 1m above the trench edge and be secured against displacement
• For wider excavations or longer duration works, consider ramped access or proprietary stairway systems

Inspections

CDM 2015 Schedule 3 requires inspections by a competent person:

• At the start of every shift before anyone enters the excavation
• After any event likely to have affected stability (heavy rain, frost, nearby vehicle movements, vibration from adjacent works)
• After any accidental fall of rock, earth, or material into the excavation

Inspection results must be recorded in writing. Include the condition of trench support, water levels, ground conditions, edge protection status, and any remedial actions required. Keep records on site and available for inspection by the HSE.

Dewatering

Water in excavations creates multiple problems. It reduces soil stability, makes surfaces slippery, and can hide trench features and services. Your RAMS should specify:

• Pumping arrangements (submersible pump with adequate capacity)
• Discharge location (not onto adjacent land or into watercourses without permission)
• Monitoring of water levels during the shift
• Procedure for stopping work if water ingress exceeds pumping capacity

When Does an Excavation Become a Confined Space?

Not every excavation is a confined space, but deep trenches and excavations can become one. The Confined Spaces Regulations 1997 apply when an enclosed or substantially enclosed space presents a reasonably foreseeable risk of serious injury from hazardous conditions.

In practice, an excavation is likely to be a confined space when:

• It is deeper than approximately 1.2m with restricted access and egress (narrow trench, limited ladder positions)
• There is a risk of gas accumulation, for example methane from contaminated or landfill ground, CO2 from decomposing organic material, or heavier-than-air gases settling at the bottom of the excavation
• There is a risk of oxygen depletion, for instance from displacement by other gases or from biological processes in waterlogged ground
• There is a risk of flooding that could trap workers

If the excavation meets confined space criteria, your RAMS must include continuous gas monitoring (4-gas detector as a minimum for O2, LEL, CO, H2S), a written rescue plan, trained rescue personnel on site, and appropriate rescue equipment. No one should enter until atmospheric testing confirms it is safe.

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Related Guides

• Confined Space Risk Assessment: UK Guide
• Construction Phase Plan: Complete UK Guide
• CDM Regulations 2015: What You Need to Know
• What is a RAMS? Complete UK Guide

Ground Conditions and Soil Types

Before any excavation begins, you must understand the ground you are digging into. Soil type is one of the biggest factors in determining how stable an excavation will be, what support systems are needed, and how quickly conditions can change.

Clay (Cohesive Soil)

Clay is a cohesive soil that tends to stand well when dry. It holds its shape and can give a false sense of security. However, clay becomes unstable when wet, swelling and softening until trench walls can collapse without warning. Seasonal changes and prolonged rainfall dramatically affect clay stability. Always reassess after wet weather.

Sand and Gravel (Non-Cohesive Soil)

Sand and gravel are non-cohesive soils that flow freely when disturbed. These are the most dangerous soil types for excavation work. They offer almost no natural support and will collapse rapidly, especially when dry or when water drains through them. Shoring or battering back to a safe angle is essential from the outset.

Made Ground and Fill

Made ground (also called fill) is completely unpredictable. It may contain a mix of materials including rubble, old foundations, voids, and buried obstructions such as disused services or storage tanks. You cannot rely on it to behave consistently. Trial holes and a thorough site investigation are necessary before committing to a method of work.

Rock

Rock is generally stable, but never assume it is safe without inspection. Check for fissures, loose faces, weathered seams, and bedding planes that could release blocks into the excavation. Mechanical breaking of rock can also destabilise adjacent ground.

Waterlogged Ground

Waterlogged ground requires dewatering before anyone enters the excavation. Common methods include sump pumps (collecting water at a low point and pumping it out) and well pointing (lowering the water table using a series of small wells around the perimeter). Dewatering must run continuously, and backup equipment should be on site.

Understanding your soil type is not optional. It directly determines your shoring requirements, safe angles of batter, inspection frequency, and the overall method statement for the excavation.

Working Near Existing Structures

Excavating close to buildings, walls, and other structures introduces serious risks. Ground removal can undermine foundations, trigger settlement, and cause structural damage that may not become apparent until weeks later.

Undermining Foundations

The key principle is maintaining the 45-degree angle of repose from the base of any adjacent foundation. If your excavation falls within this zone, you risk undermining the structure. In practice, this means drawing a 45-degree line from the bottom of the nearest foundation down into the ground. Your dig must not encroach into that triangle of influence.

Party Wall Agreements

If the excavation is within 3 metres of a neighbouring property's structure (or 6 metres if the excavation would cut below the bottom of that structure's foundations), a party wall agreement under the Party Wall etc. Act 1996 will likely be required. This must be arranged before work starts.

Temporary Propping

Where excavation unavoidably affects adjacent structures, temporary propping may be needed to support the structure while ground is removed. This must be designed by a structural engineer and installed before any undermining takes place.

Vibration Monitoring

Vibration monitoring should be in place when using heavy excavation plant near existing structures. Hydraulic breakers, vibratory rollers, and even tracked excavators can transmit damaging vibrations through the ground. BS 5228-2 provides guidance on acceptable vibration levels for different building types.

Crack Monitoring

Install crack monitoring (tell-tales or demec studs) on existing buildings before excavation begins. Photograph and record existing defects in a condition survey. This protects both you and the building owner by providing a clear before-and-after record.

Reduced Dig Zones Near Retaining Walls

Excavating near retaining walls is particularly high risk. Removing ground on the retained side reduces passive resistance and can trigger wall failure. A structural assessment of the retaining wall is essential before any excavation within its zone of influence.

Contaminated Land

Brownfield sites and land with previous industrial use may contain hazardous materials that pose serious risks to excavation workers. Contamination is not always visible or detectable by smell, making desk-based research and laboratory testing essential before breaking ground.

Common Contaminants

• Asbestos in made ground, demolition rubble, or buried waste
• Hydrocarbons from fuel storage, vehicle maintenance, or industrial processes
• Heavy metals such as lead, arsenic, chromium, and cadmium from manufacturing or tanning
• Landfill gas (methane and carbon dioxide) from decomposing organic material
• Unexploded ordnance (UXO) on sites with wartime history, particularly in urban areas that experienced bombing

Desktop Study and Site Investigation

A desktop study (Phase 1) reviews historical maps, environmental databases, and previous site uses to identify potential contamination. Where risks are identified, a site investigation (Phase 2) involves boreholes, trial pits, and laboratory analysis of soil and groundwater samples. This must be completed before excavation begins.

Monitoring During Excavation

During excavation on potentially contaminated sites, continuous monitoring for volatile organic compounds (VOCs) and methane is required using portable gas detectors. Workers must be trained in reading the instruments and understanding action levels. If trigger levels are exceeded, evacuate the excavation immediately.

Disposal of Contaminated Material

Contaminated spoil cannot be disposed of as normal waste. It requires formal waste classification through WAC testing (Waste Acceptance Criteria) to determine which category of landfill can accept it. Results dictate whether material goes to inert, non-hazardous, or hazardous waste facilities. Costs escalate significantly for hazardous classification.

PPE and Decontamination

Workers on contaminated sites need additional PPE beyond standard excavation equipment. This may include disposable overalls (Tyvek suits), nitrile gloves, RPE with appropriate filters (P3 for asbestos, A2 for organic vapours), and safety goggles. A decontamination procedure must be in place, including designated clean/dirty zones, boot washes, and welfare facilities with showers.

Frequently Asked Questions

How deep can I dig without shoring?

There is no safe depth for an unsupported excavation. Even trenches as shallow as 0.6 metres have killed workers when the sides collapsed. The assumption that shallow trenches are safe is one of the most common and dangerous misconceptions in construction. Every excavation must be assessed individually based on soil type, weather conditions, surcharge loads, and the presence of water. If there is any doubt, install temporary support before anyone enters.

Do I need a permit to dig near a gas main?

Yes. Before excavating near any gas infrastructure, you must contact the gas transporter (typically Cadent, SGN, Wales & West Utilities, or Northern Gas Networks depending on your region) and obtain plans showing the location of mains and services. For work within the safety zone of a high-pressure gas main, you will need a formal permit and may require a gas company representative on site. Use Dial Before You Dig or the LSBUD (Line Search Before U Dig) service to identify all buried utilities in the area.

What is the 500mm hand-dig rule?

The 500mm hand-dig rule requires that once a buried service has been located (using a cable avoidance tool, signal generator, or trial holes), all excavation within 500mm of that service must be carried out by hand. Mechanical excavators must not be used within this zone. This applies to all buried services including gas, electric, water, and telecoms. The rule comes from HSE guidance document HSG47.

How often must excavations be inspected?

Under the Construction (Design and Management) Regulations 2015, excavations must be inspected by a competent person:

• At the start of every shift before work begins
• After any event likely to have affected stability (heavy rain, frost, vibration from nearby plant, or any fall of material)
• After any accidental fall of rock, earth, or other material

Inspection results must be recorded and kept on site. Reports should note the condition of supports, any signs of ground movement, water ingress, and the general stability of the excavation face.

Can I use the excavator bucket as an edge protection barrier?

No. An excavator bucket is not edge protection. It is not fixed, not rated for the purpose, and can be moved at any time (including accidentally). Physical edge protection such as barriers, guardrails, or stop blocks must be installed around all excavation edges where there is a risk of people or vehicles falling in. This is a requirement under the Work at Height Regulations 2005 and CDM 2015.

Authority Sources and Further Reading

The following external guidance documents provide detailed technical and regulatory information on excavation safety in the UK.

• HSG47: Avoiding Danger from Underground Services (HSE, 4th edition). The definitive guide to safe digging practices near buried utilities.
• CIS64: Preventing Excavation Collapses (HSE Construction Information Sheet). Summarises the key risks and control measures for excavation work.
• NHBC Standards Chapter 4.2: Building Near Trees. Covers foundation design requirements when working near trees and drains, including minimum depths and heave protection.
• CIRIA C760: Guidance on Embedded Retaining Wall Design. Technical guidance on the design, construction, and monitoring of embedded retaining walls in excavations.

For related risk assessment templates and construction safety guides, see these resources on our site:

• Confined Space RAMS: Complete UK Safety Guide
• Construction Phase Plan: Complete UK Guide
• Working at Height RAMS: Complete Safety Guide
• What is a RAMS Document? Complete UK Guide
• CDM Regulations 2015: What You Need to Know