Excavation work generally means work involving the removal of soil or rock from a site to form an open face, hole or cavity using tools, machinery or explosives.
A person conducting a business or undertaking must manage risks associated with all kinds of excavations at the workplace, no matter how deep.
Specific duties apply in relation to the higher-risk excavations, such as trenches, shafts and tunnels. However, these requirements do not apply to a mine, a bore to which a relevant water law applies or a trench used as a place of interment.
Any construction work (including any work connected with an ‘excavation’) that is carried out in or near: a shaft or trench with an excavated depth of greater than 1.5 metres, or a tunnel is considered to be ‘high risk construction work’ for which a safe work method statement (SWMS) must be prepared.
Further guidance on the duties related to high risk construction work and SWMS is available in the Code of Practice: Construction Work.
source: https://www.safeworkaustralia.gov.au/system/files/documents/1705/mcop-excavation-work-v1.pdf