In recent times there has been an increase in the number of employees who have lost their lives during excavation operations. This is due to either being buried alive in excavations or material falling opon employees such as walls when doing excavations near structures.

This article aims to assist those frequently working in excavations and how to safeguard themselves when doing so.

What you need to do:

Construction Regulation 13 states that you must prevent danger to workers in or near excavations. To maintain the required precautions, a competent person must be appointed in writing to inspect excavations at the start of the working shift and at other specified times. No work should take place until the excavation is safe.

Commercial clients must provide certain information to contractors before work begins. This should include relevant information on:

• Ground conditions- Geotechnical reports.
• Underground structures or water sources.
• The location of existing services.
• This information should be used during the planning and preparation for excavation work.

Key issues are:

• Collapse of excavations.
• Falling or dislodging material.
• Falling into excavations.
• Inspection.

What you need to know:

Every year people are killed or seriously injured by collapses and falling materials while working in excavations. They are at risk from:

• Excavations collapsing and burying or injuring people working in them.
• Material falling from the sides into any excavation.
• People or plant falling into excavations.

Remember:

• No ground can be relied upon to stand unsupported in all circumstances.
• One cubic metre of soil can weigh as much as one tonne.

Trenchless techniques should always be considered at the design stage as they replace the need for major excavations.

Underground and overhead services may also present a fire, explosion, electrical or other hazard and will need to be assessed and managed.

Collapse of excavations
Temporary support – Before digging any trench pit, tunnel, or other excavations, decide what temporary support will be required and plan the precautions to be taken.
Make sure the equipment and precautions needed (trench sheets, props, baulks etc) are available on-site before work starts.

Battering the excavation sides – Battering the excavation sides to a safe angle of repose may also make the excavation safer.

In granular soils, the angle of slope should be less than the natural angle of repose of the material being excavated. In wet ground, a considerably flatter slope will be required.

Falling or dislodging material

Loose materials – may fall from spoil heaps into the excavation. Edge protection should include toeboards or other means, such as projecting trench sheets or box sides to protect against falling materials. Head protection should be worn.

Undermining other structures – Check that excavations do not undermine scaffold footings, buried services or the foundations of nearby buildings or walls. Decide if extra support for the structure is needed before you start. Surveys of the foundations and the advice of a structural engineer may be required.

Effect of plant and vehicles – Do not park plant and vehicles close to the sides of excavations. The extra loadings can make the sides of excavations more likely to collapse.

Falling into excavations

Prevent people from falling – Edges of excavations should be protected with substantial barriers where people are liable to fall into them.

To achieve this, use any of the below:

• Guard rails and toe boards inserted into the ground immediately next to the supported excavation side.
• Fabricated guard rail assemblies that connect to the sides of the trench box.
• The support system itself, e.g. using trench box extensions or trench sheets longer than the trench depth.

Inspection

A competent person who fully understands the dangers and necessary precautions should inspect the excavation at the start of each shift.

Excavations should also be inspected after any event that may have affected their strength or stability, or after a fall of rock or earth.

A record of the inspections will be required and any faults that are found should be corrected immediately.

Construction Regulation 13

Construction Regulation 13 requires the following to be in place regarding excavations on site:

• Excavation supervisor appointed in writing.
• Written permission issued by the supervisor to work in an excavation where there no need for shoring and/or bracing.
• Steps taken to ensure that the shoring or bracing contemplated in 13(2)(b) is designed and constructed in a manner that renders it strong enough to support the sides of the excavation in question.
• Register up to date.

Source: Construction Regulations

Neil Enslin | Occupational Health and Safety Manager