Mechanism and early-warning methods of roadway roof fall in coal seam

Roof disasters are the most frequent and deadliest among all kinds of disasters in coal mines in China.At present, most roof accidents happen in roadway, especially the roadway in coal seam affected by mining.Based on the relationship analysis between roof accidents and surrounding rock environment, the roadway roof fall in coal seam is divided into two main types:surrounding rock dominant type and stress dominant type.The mechanism and causes of the roadway roof fall for the fractured critical rock falling, friable rock mass falling, weakly bonded composite roof collapsing and butterfly leaf typed roof falling in large deformation roadway are revealed.Then a multi-stage and full time warning method for roadway roof fall is proposed, namely, the long-term risk assessment of the roof fall hidden dangers in the roadway design stage, ever-present prediction with drilling in the roadway excavation stage and a long time critical early warning in service cycle.The instruments and equipment for long and critical early warning are developed, such as the drilling detector for rock structure, roof multipoint displacement monitor and monitoring, and alarm device for anchor cable working condition.The mechanism of roadway roof fall in coal seam, warning method and various instruments and equipment would provide theoretical support and tech-nical support for the prediction and prevention of roof accidents.