In April 2020, a development drill rig (jumbo) operator and fitter were injured when a 750 kg rock fell from a height of approximately five metres from the face of an access development heading, striking both workers.
The fitter received serious injuries. The workers were approaching the face of the second cut to install lifter tubes into the lifter holes of the last two rows of blast holes. At the time, most of the face had been bored with only the last two rows remaining. The first cut was taken the day before in a single blast, from top fillet to bottom fillet using a drag round and 4.9 m drill steel.
Direct causes
The rock dislodged from the bored face, from a geological structure, striking the two workers approaching the face to install lifter tubes.
Contributory causes
- Use of an out-of-date rock mass model to assess the design.
- The planning and design process did not consider local geotechnical information at the newly established heading.
- Geological information was not available for the development heading due to infrequent mapping.
- Geotechnical inspections were not completed as per the Ground Control Management Plan.
- A large number of geological structures that indicate the presence of blocky ground were not identified prior to the incident.
- Excessive material fell from the backs during scaling, indicating the presence of poor ground conditions, however additional ground support was only installed on the side wall leaving the face unmeshed.
- Development methodology and jumbo setup resulted in rows on the face bored before all the lifter tubes had been installed.
- A 4.9 metre drill steel was used to establish the heading and may have impacted on directional control within fractured or blocky ground resulting in excessive damage to the perimeter and face.
- Inadequate inspections by competent person(s) before commencement of drilling.
- Lack of training in geotechnical hazard awareness.