Duty holders must follow the hierarchy of control under the WHS Regulations for certain risks, and it can be used for any risk. The first aim is elimination, for example doing work above ground so no trench, tunnel or shaft is needed. If that is not reasonably practicable, the risk must be minimised by one or more of: substitution (for example an excavator fitted with a rock breaker instead of manual breaking); isolation (for example concrete barriers keeping pedestrians away from powered mobile plant); and engineering controls (shoring the sides, or benching or battering them, so they cannot collapse). Any remaining risk must then be minimised by administrative controls as far as reasonably practicable, such as warning signs near the excavation, and finally by suitable PPE such as hard hats, hearing protection and high visibility vests. Administrative controls and PPE do not act on the source and depend on behaviour and supervision, so alone they are the least effective. Chapters 4 to 6 describe excavation controls.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.