Application of outburst risk indices in the underground coal mines by sublevel caving

The underground coal mines of Hullera Vasco Leonesa SA (HVL) have exhibited sudden emissions of methane called “blows” and “outbursts”. A research study has been conducted in order to analyse those risk indices with a greater impact on the prediction and control of outbursts in a heading driven in a coalbed located 17 m below a roadway in which the shortwall and sublevel caving method is being employed. Extensive measurement programmes have been carried out in an operating coal mine, both in the heading face and in the coal above it. Coal samples have been analysed and tested in the laboratories of HVL.The aim of this study is to analyse the advantages and drawbacks of the chosen indices, their relationship with operating parameters such as distance between the heading face and the shortwall face, height difference between both levels, heading face and roadway, optimization of the different borehole degasification patterns and water injection in those boreholes. It is concluded that a simple methodology to predict and control sudden methane outbursts has been developed and put into practice in HVL. This methodology is based on the mentioned indices and it can be partially or totally extrapolated to other underground coal mines.

► Application of easy-to-use indexes in the prediction of outbursts.
► Desorption velocity (V1) and gas pressure in the coalbed predict outbursts correctly.
► Degasification by boreholes and water injection diminish the possibility of outbursts.
► The sublevel caving method in an upper roadway degasses the heading located 17 m below.