Excavation Support Systems: Choosing the Right Method for Your Site

Table of Contents

• Why Getting Excavation Support Right Matters
• Trench Boxes and Hydraulic Shoring
• Sheet Piling
• Battering and Benching
• Bored Pile Retaining Walls
• Temporary Works Design Requirements
• RAMS Documentation for Excavation Support
• Frequently Asked Questions
• Next Steps

Why Getting Excavation Support Right Matters

Trench and excavation collapses kill and seriously injure workers on UK construction sites every year. The HSE consistently identifies excavation as one of the highest-risk activities in the industry. Most fatalities occur in excavations that were either unsupported or supported inadequately — and in many cases, the collapse happened without warning.

Choosing the right support system and documenting it correctly in your RAMS is therefore not a bureaucratic exercise. It is the primary mechanism by which operatives working in or near excavations are protected. This guide helps you understand the options available, how to select the right one for your site conditions, and what you need to document.

For a complete guide to bulk excavation RAMS requirements, see our bulk excavation and earthworks RAMS guide.

Trench Boxes and Hydraulic Shoring

Proprietary trench boxes are the most common support method for linear excavations such as drainage trenches, foundation trenches, and service corridors. They work by squeezing against both sides of the trench to provide lateral support, with hydraulic props connecting the two sides.

When trench boxes are appropriate:

• Linear trenches up to approximately 6 metres deep (depending on the box type and ground conditions)
• Stable, cohesive ground conditions (medium to stiff clays)
• Where the excavation width allows the box to be installed
• Where the trench can be advanced by the box being installed ahead of excavation or by sliding the box along the trench

Limitations:

• Not suitable for loose granular soils or running sand unless supplemented with close-sheeting
• Not suitable for excavations with surcharge loads from adjacent plant or structures that exceed the box's rated capacity
• The manufacturer's rated capacity must be verified against site-specific soil parameters

Your RAMS must confirm the box type, its rated capacity, that it has been inspected and certified, and that the site conditions are within its design parameters.

Sheet Piling

Steel sheet piling provides a continuous interlocking wall of steel driven or pressed into the ground before excavation commences. It can function as both temporary works and permanent retention.

When sheet piling is appropriate:

• Deep excavations (typically 4+ metres)
• Excavations in granular soils or below the water table, where trench boxes are not adequate
• Excavations adjacent to existing structures or services where ground movement must be minimised
• Where the sheet pile wall will become part of the permanent works

RAMS requirements for sheet piling:

• Sheet pile wall design by a competent Temporary Works Designer (or Permanent Works Designer if the piles are permanent)
• Pile installation method (impact hammered, vibrated, or hydraulically pressed) and the implications for noise, vibration, and adjacent structures
• Propping or anchoring design (sheet piles are typically propped back at intervals as excavation proceeds)
• Monitoring requirements for ground movement and prop loads
• Extraction plan for temporary piles (if applicable)

Battering and Benching

Reducing the angle of excavation faces to a stable slope (battering) or forming stepped excavation profiles (benching) is the simplest form of excavation support and avoids the need for installed systems. However, it requires significant additional space and is only appropriate where site conditions allow.

Stable slope angles depend on soil type:

• Stiff intact clay — slopes up to 45° may be stable in the short term, but softening over time reduces this
• Granular soils — the stable angle is approximately equal to the angle of friction (typically 25-35°)
• Fill and mixed soils — assume a conservative angle until tested
• Below the water table — battering alone is rarely adequate; dewatering is required

Battering slopes must be inspected daily and after rainfall by a competent person. Any signs of cracking, slumping, or seepage must be investigated before work continues. Your RAMS must specify the slope angles used, the basis for them (geotechnical advice), and the inspection regime.

Bored Pile Retaining Walls

Secant and contiguous piled walls consist of rows of interlocking (secant) or closely spaced (contiguous) bored piles forming a continuous or near-continuous wall. These are used for deep excavations (typically 6+ metres) where sheet piling is not practical or where ground movement must be tightly controlled.

RAMS requirements:

• Reference to the permanent or temporary works design for the piled wall
• Confirmation that the piling RAMS (addressing rig stability, services, etc.) are separate from and referenced by the earthworks RAMS
• Propping design as excavation proceeds (typically reinforced concrete props or steel tubular props)
• Monitoring and trigger levels for wall movement and prop loads

Temporary Works Design Requirements

All excavation support systems except simple battering within known stable slope angles require a Temporary Works Design by a competent Temporary Works Designer and an independent check by a Temporary Works Coordinator. The design must:

• Be based on the site-specific ground investigation data
• Consider all surcharge loads from plant, materials, and adjacent structures
• Address groundwater conditions
• Specify the installation and removal sequence
• Define inspection requirements and trigger levels

Under BS 5975 (Code of Practice for Temporary Works Procedures), the Temporary Works Coordinator role must be formally assigned. Your RAMS should record who holds this role for the project.

RAMS Documentation for Excavation Support

Your RAMS for excavation support must include:

• The support method selected and the basis for the selection
• Reference to the Temporary Works Design and the designer's details
• The installation sequence and any constraints on the excavation sequence
• Inspection regime (daily as a minimum, plus after rain or any event that may affect ground conditions)
• Trigger levels for remedial action
• Emergency procedure for signs of movement or incipient collapse
• Competency of operatives installing and inspecting the support

Frequently Asked Questions

Who can sign off excavation support as adequate?

A "competent person" under the Construction (Health, Safety and Welfare) Regulations must inspect excavations before each shift, after any event likely to have affected stability (heavy rain, frost, adjacent works), and after any accidental fall of material. For anything beyond simple battering, the competent person should have specific geotechnical knowledge. The Temporary Works Designer is responsible for the design; the site supervisor is responsible for ensuring it is installed and maintained correctly.

Can I use a second-hand trench box without manufacturer documentation?

Not safely. A trench box without manufacturer documentation (rated capacity, inspection records, maintenance history) cannot be assumed to be safe to use. Before using any second-hand shoring equipment, obtain a thorough examination from a competent person and confirm the rated capacity is appropriate for your ground conditions. Document this examination in your RAMS.

When does excavation support also need Building Regulations approval?

If the excavation is part of a notifiable building project, the excavation support may be subject to Building Regulations approval (Part A — Structure) if it forms part of or directly loads the permanent works. Discuss with your principal designer and structural engineer at the design stage. For temporary excavation support that leaves no permanent component, Building Regulations do not typically apply, though Local Authority notification under CDM may still be required.

Next Steps

Browse all trade RAMS templates on the RAMS AI trade hub — covering 22 specialist construction trades.

Selecting and documenting excavation support correctly is one of the most important steps in protecting your operatives and complying with UK health and safety law. RAMS AI helps you produce comprehensive, compliant RAMS for all types of excavation and earthworks operations.