Problems encountered with the Old Ben system prompted the design of Wongawilli system of Pillar extraction, and the following parameters were set:
1. Provision of a single working place
2. Extraction of coal in stress relieved areas
3. Utilisation of the coal in stress as a support
4. Maximise extraction of the seam, and
5. A system that was simple and readily understood by all employees.
The method provides;
a) A straight goaf line
b) Simple ventilation system, with air being coursed via the goaf, and
c) Working within destressed areas.
The key to its success was working within, and using destressed areas to the full advantage. It has been possible to use this method at depths of up to 600 meters. Model test and mathematical simulations have been performed to arrive at the stability required. It should be noted that horizontal stresses play a major part in the contributing factors that give rise to deterioration of roadways and intersections.
The production and productivity of the method using the continuous miner and shuttle cars was in the order of 500 tonnes per shift, particularly during fender lifting.
The Wongawilli method has, in the past, been used for mining coal both in advance and retreat.