Both sets of rear wheels on a dump truck dropped approximately 1m when the edge of the dump slumped while the operator was tipping the load.
The NSW Resources Regulator said ground stability should be a primary consideration when designing a dump.
"Material consistency, wet conditions and dipping ground stability should be considered," it said.
"Inspections should verify dump integrity.
"Areas that do not meet the standard should be demarcated, communicated and remediated to meet the standard."