State Environmental Planning Policy (Exempt and Complying Development Codes) 2008

(10) Support for earthworks more than 600mm above or below ground level (existing) must take the form of a retaining wall or other structural support that— (a) a professional engineer has certified as structurally sound, including in relation to (but not limited to) its ability to withstand the forces of lateral soil load, and (b) has been designed so as not to redirect the flow of any surface water or groundwater, or cause sediment to be transported, onto an adjoining property, and (c) has adequate drainage lines connected to the stormwater drainage system for the site, and (d) does not result in a retaining wall or structural support with a total height measured vertically from the base of the retaining wall or structural support to its uppermost portion that is more than the height of the associated excavation or fill, and (e) is separated from any retaining wall or structural support on the site by at least 2m, measured horizontally, and (f) has been installed in accordance with the manufacturer’s specifications (if any), and (g) if it is an embankment or batter—has a toe or top that is more than 1m from any side or rear boundary.