An excavator operator excavating coal was seriously injured when a rock fall occurred and struck the excavator. The operator was in the excavator cab at the time of the incident. The matter is currently under investigation by WorkSafe New Zealand.

[image] ground failure incident.
Figure 1 : Excavator after the rockfall.

While WorkSafe has not reached any conclusions in that investigation, it is timely to remind the extractives industry of the need to ensure effective controls are in place to manage ground instability hazards.


Ground instability hazards management in mines and quarries is a critical risk area the sector must address through having effective controls which are continuously monitored to ensure they remain effective.

All critical risk controls must be understood by all workplace personnel and applied without exception to ensure everybody’s safety.

Designing a mine or quarry to enable safe product extraction is a fundamental principle of an extractives operation. This can be achieved by:

  • undertaking a geotechnical assessment to identify the geotechnical properties of the excavation material
  • establishing overall slope design with an appropriate safety factor
  • designing of bench heights and widths
  • optimised orientation of rock faces including identifying failure modes to minimise rock falls
  • design enough space for windrows, rock traps and roads
  • ensuring excavators and other equipment are appropriate for the specific mine layout.

Following the identification of ground or strata instability as a principal hazard, the senior mining operation site executive must ensure a geotechnical assessment is completed by a competent person to determine what ground or strata support level is required for safe mining. They must also ensure there is a principal hazard management plan (PHMP) for ground or strata instability in place.

The PHMP and associated geotechnical assessments must be reviewed and revised where necessary when a material change in ground conditions has occurred, or excavation methods changed.

Effective ground control relies on geotechnical information obtained throughout the site’s life-cycle:

  • during planning and design
  • at design implementation and
  • during day-to-day operations.

Where an existing design has already been proved, it may be used as the basis for new excavation design, where ground conditions at both sites are similar. 

What else should I be doing?

Use our guidance on Health and Safety at Opencast Mines, Alluvial Mines and Quarries to assist in development and implementation of a PHMP for ground or  strata  instability.

Consider options to fit operator protection to mobile plant in which operator is at risk of cabin intrusion or falling objects. 

More information

WorkSafe Extractives Safety Alert on Quarry operations - Highwall failure causing death

Authorised by Mark Pizey, Chief Inspector Extractives 

Issued by WorkSafe New Zealand