Observations and classification of roof strata behaviour over longwall coal mining panels in India

A study has been made of a number of mechanized longwall panels in various coal mines in India, concentrating on the geology, physico-mechanical rock properties and the behaviour of the coal measure roof rocks during mining. The research has highlighted the splitting and caving characteristics of the strata rocks and enabled the development of a roof-rock classification system. Roof rocks are classified into six categories based on the: (a) mean weighted uniaxial compressive strength; (b) RQD; (c) (i) type of rocks, (ii) presence of cracks, fissile beds, splitting, etc., (iii) presence of water; and (d) thickness of bed layer. The behaviour of layers and composite layers in the immediate roof rock mass is also enumerated. Relations between the rock strength properties and values for the bulking factor of the failed rock are included. The concepts of a ‘weighting zone’ and ‘caving zone’ are proposed. The paper also clarifies the occurrence of different types of failure, such as periodic falls. All these findings should be helpful during calculation of the powered support capacity.