Prediction and prevention of sandstone-gas outbursts in coal mines

Abstract

Rock-gas outbursts, including sandstone-gas outbursts, become more and more serious with increasing depth of engineering and more difficult geological environments and their prediction and prevention are one of the major challenges to the rock mechanics and rock engineering community. Comparatively speaking, sandstone-gas outbursts have not been well studied and are less documented than coal-gas outbursts. So the exchange of information, especially in the field of the prediction and prevention of sandstone-gas outbursts, is important. This paper outlines an outburst in which over 2000 tonnes of oil-bearing sandstone were ejected with 900,000 m 3 of gas in the air shaft of Haishiwan Colliery; this is the largest sandstone-gas outburst in China to date. The theoretical and technical investigation relating to the prediction and prevention of such sandstone-gas outbursts, taking the Haishiwan Colliery project as the background, are described in the paper. A comprehensive prediction method employing a suite of macro- and micro-indices gained from test drilling and laboratory testing on rock cores is proposed in the paper. It is found that the combination and comparison of the results of field observations, measurements and laboratory tests are helpful to ensure the reliability of outburst prediction. The principle and scheme of preventive drilling and discharging, including the pattern and number of releasing boreholes and the safety distance for drilling, were studied. It is revealed that discharging of gas can also release rock mass strain energy, which should be taken into consideration in the determination of the number of releasing boreholes. For the purpose of releasing, the Tubular Destressed and Depressurized Protective Zone (TDDPZ) pattern proposed in the paper is more efficient and economical than the currently applied fan-shaped pattern of releasing boreholes. The accuracy of prediction and the efficiency of the preventive measures were verified by successful excavation through the oil- and gas-bearing sandstone units in Haishiwan Colliery.