Wilpinjong Coal Mine uses dozers to remove overburden
and in 2015 implemented a semi-autonomous dozer program
to improve the efficiency of this process.
The semi-autonomous tractor system (or SATS) consists of
four modified dozers which can be operated remotely or in
a semi-autonomous state by an operator in the control station.
On the 27th of May 2019, an operator returned to
an excavator after being on break.
The excavator was being used to scale a section of a
highwall at the rear of the operating area of the
semi-autonomous dozer fleet.
The excavator was working behind a windrow which stopped
midway along the dozer operating area.
Earlier in the shift, a small bund had been constructed
between the windrow and the highwall,
as a barrier to the work area.
Throughout the shift, the dozers had driven through this bund,
and it had been levelled.
At about 1:40pm, the excavator operator travelled past the
levelled windrow, into the active work slot of a dozer.
As the dozer had completed a push, it started reversing.
The dozer was travelling in second gear at approximately
7 kilometres per hour.
As it got to the end of the slot, it collided with the
rear of the excavator.
The dozer pushed the excavator
approximately 1.5 metres sideways.
The excavator operator attempted to call the
SATS operator on the radio, to stop the dozer.
He was unsuccessful.
Five seconds after losing traction, the system identified
that it had experienced track slip and stopped tramming.
From initial contact, to the dozer stopping,
took approximately 14 seconds.
An emergency response was activated.
The excavator operator was not injured.
The investigation into the incident identified
the following causal factors:
The controls implemented were found to be unreliable
and prone to human error,
such as the separation bund.
There was a lack of engineering controls
such as proximity awareness to allow detection of
manned excavators by the SATS system and
SATS operator.
There was a lack of engineering controls such as
collision avoidance systems to prevent collisions between
manned and autonomous equipment.
The height of the windrow prevented the excavator
operator sighting the SATS dozers in the work area.
The communication between the excavator operator and SATS
operator did not clearly identify the work areas
of the SATS dozers.
The bund used to separate the work areas was not maintained
and became ineffective.
Following the incident, the mine operator fitted a proximity
awareness system to their excavators.
The proximity awareness system allows the SATS
dozers and operators to monitor machines and apply
two virtual barriers.
When the first barrier is breached, it triggers an alarm.
When the second barrier is breached, the dozer stops,
preventing a collision.
The mine operator fitted an autonomous stop system
to their excavators.
Should all else fail, this system allows the
excavator operator to remotely stop all SATS dozer operations
from the cabin of the excavator.
The mine operator requires
workers to carry a portable autonomous stop device
when entering the autonomous operations area on foot.
The mine operator also implemented procedural changes
that included:
Creating guidelines for workers in the SATS operation area.
Defining minimum separation distances between manned
equipment and SATS dozers.
Creating a process for the testing and allocation of
A-Stop devices.
For more information and to see the full report,
visit our website.