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CROSS Safety Report

Lift pit excavation hazards

Report ID: 821 Published: 1 July 2019 Region: CROSS-AUS

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A reporter came across an unsafe deep excavation and asks how a geotechnical engineer views the risk of excavation collapse.

A construction worker took an unacceptable risk when standing next to an unprotected deep excavation without any obvious safety measures.

Key Learning Outcomes

For structural and civil engineers:

  • Be aware of potential dangers created by deep excavations,and try to eliminate or at least reduce any risks by modified designs, as appropriate

  • Design temporary shoring for the sides of excavations more than 1.5m deep

For construction professionals working or attending on site:

  • Recognise the possibility of unstable side walls of deep excavations

  • Ensure that any workers who need to approach the edge of such excavations have adequate safety equipment and training

  • Be aware that collapse of deep excavations could result in serious injury or death, possibly leading to prosecution for industrial manslaughter

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The reporter took the attached photo (Figure 1) of a worker standing close to the edge of a deep excavation.

Figure 1: lift pit excavation hazards

Identified hazards

The reporter notes that there are several issues/risks here:

  1. Worker safety from falling into the pit which may have had water and slurry in it.

  2. There was no immediate escape method visible (except perhaps via the excavator bucket?).

  3. Excavation side wall collapse.

  4. The stockpiles to the side are a potential risk although they were being moved at the time.

Control measures for safety

The controls for all of the above are or should be well known by builders. For example:

  1. Worker fall restraint could be achieved by harness systems or a walkway with handrails etc.

  2. An access ladder should be available.

  3. In NSW, the excavation code of practice requires that "Shoring, benching and/or battering may not be required if written advice is received from a geotechnical engineer that all sides of the trench are safe from collapse. Any advice should state the period of time to which it applies and may be subject to a condition that specified natural occurrences may create a risk of collapse."

The reporter would be interested to hear more from a geotechnical engineer on how they look at the risk of excavation collapse.

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Despite much publicity about this issue, deaths from excavation collapses are all too common and may now lead to corporate manslaughter charges as has happened in the UK. In Australia, industrial manslaughter offences now exist in Queensland and the ACT.

The reporter draws attention to the NSW Excavation work code of practice - and other states and territories have similar codes that are based on the Safe Work Australia Code of Practice for Excavation Work.

High risk when depth more than 1.5m

All parties involved in construction work, including structural engineers, must address workplace health and safety issues and while any excavation is a hazard, the above codes of practice consider any excavation over 1.5m deep to be high risk and requiring control measures to prevent collapse unless a geotechnical engineer has advised otherwise.

Elimination/reduction of risk through design

This is also a design matter and clause 3.2 in the above code of practice sets out the responsibilities of designers, including “Designers of structures should consider possible excavation work methods and health and safety control measures when producing any final design documents and the safety report for the structure.”

As the reporter notes, it would be good to receive feedback on how a geotechnical engineer would address the question of when control measures are not required. If you can provide feedback on this, or any other report, please submit feedback on the CROSS-AUS website.

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