Coal mines 22 Coal 11 coal mining 9 Coal-mining 8 Technology: general issues 8 Coal deposits 7 History of engineering and technology 6 China 4 Coal seams 4 Numerical models 4 Rocks 4 Coal production 3 Decision making 3 Numerical methods 3 Research & information: general 3 % reductions 2 Bolts 2 Case-studies 2 Concrete construction 2 Damage detection 2 Deep tunnels 2 Disability: social aspects 2 Distinct element methods 2 Ecology 2 Economic history 2 Ecosystems 2 Electric power generation 2 Environmental economics 2 Environmental management 2 Forecasting 2