OHS Code Explanation Guide

Published Date: July 01, 2009
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Part 32 Excavating and Tunnelling

Section 443 Soil stabilization

Subsection 443(1)

The OHS Code defines an excavation as a dug out area of ground that does not include a tunnel, underground shaft or open pit mine. As a result, a trench is considered to be a type of excavation having one special feature – it is deeper than its width at the bottom. Where the term “excavation” is used in this Part, it is meant to include trenches unless otherwise stated.

Subsection 443(2)

A number of artificial stabilization techniques are acceptable as alternates to shoring an excavation, tunnel, underground shaft or open pit mine. Artificial methods such as freezing or grouting (injecting a chemical or cement grout into the voids of pervious soils, allowing the injected material to solidify and form an impervious barrier to groundwater), may require defined periods of time in which to “set”. Once “set”, the soil is stable.

If not properly designed by a professional engineer and performed as designed, a risk to workers may still be present. It is therefore mandatory that a professional engineer design any artificial soil stabilization process. The employer is responsible for ensuring that the professional engineer’s specifications are followed.

Subsection 443(3)

Natural freezing is subject to changing temperature and weather conditions and cannot be controlled. Even if the soil is frozen to a specified depth, fluctuating temperatures could result in unexpected or unplanned thawing of surface layers. As such, the structural integrity of the excavation could be compromised and the risk to workers significantly increased. Natural freezing as a means of soil stabilization is therefore unacceptable under any circumstances.