According to chief scientist at the China Coal Research Institute professor Guofa Wang since top coal caving has been adopted in China the single yield record of a working face has improved continuously.

“The top coal caving method of mining is the best mining for complex geological conditions and also an effective approach to achieving high-production and efficient mining process,” Wang said in his paper ‘The development of longwall mechanised mining, strata control and technology of powered supports’

Top coal caving has become somewhat of a hot topic in Australia, recently recognised in ACARP’s 2004 funding of underground coal mining research projects. The project just approved, Longwall Top Coal Caving Application Assessment In Australia aims to develop design tools and technology to facilitate the application of the longwall top coal caving method in Australia. The project will develop a geotechnical top coal caving model and assessment procedure, an understanding of the environmental hazards and an optimum top coal mining process model.

Top coal caving practice is continuing to expand in China and is also tackling new frontiers, including application into medium had coal seams, “three flexible” coal seams and thinner coal seams. It has also been applied in hard coal seams, shallow coal seams and other geological conditions.

In one example, top coal caving was used at the Wangjiashan mine with a coal seam incline angle of 35 to 42 degrees and a thickness of 15 to 12 metres. In 2002 the mine achieved a yield on a single working face of 60,000 ton per month and a worker productivity of 45 ton/worker. Coal recovery of the seam was more than 80%.

Wang said there were several stand out advantages top coal caving had to offer including: the adaptability to geological conditions in top coal caving is stronger; it achieves greater recovery of the coal seam resource and productivity is high; and the cost is low and the economic benefits are significant.

During the 20 years China has used top coal caving, major leaps in technology and understanding have been made. Strata behaviour has been extensively studied along with the structures of top coal, and immediate roof and overlying strata have been described. Wang said calculation formulas for the setting and yield pressures for supports have also been developed.

The adoption of powered supports and equipment to top coal caving has been successfully adapted to different types of geological conditions. Researchers have also explored several different types of high-production and high-efficiency processes.

Coal recovery approaches have been improved after a quantity analysis study of losses of top coal into the goaf.

Wang said the mechanism of gas release has also been enhanced, thus decreasing the possibility of coal self-ignition.

The technology of anchor bolt support in coal roadways has been improved though mechanical testing, selection of material for bolt anchor and monitoring technology of bolt anchor.