Roof Catastrophe Mechanism of Roadways with Extra-thick Coal Seam and its Controlling Countermeasures

This paper focuses on the control of roof caving, which happens frequently in the roadway support for extra-thick coal seam during the mining activities. Combined with theoretical analysis, field investigation, numerical simulation and field test, the roof catastrophe mechanism of roadways with extra-thick coal seam and key factors influencing the bedding separation in the roof strata are concluded, and then an innovative prevention and control approach for the roof caving disaster of coal roadways with extra-thick coal seam is proposed, which consists of a set of control system for the roof stability and a safety evaluation system. The following conclusions and achievements are obtained in this study. (1) It is concluded that the main reason for roof caving accidents of coal roadways with extra-thick coal seam in underground mines is that extra-thick coal seam contains multiple interlayers in soft rock strata and concentrates discrete structures like bedding and joint fissures. The catastrophe development of roof caving disaster is in order of bedding separation, fracture, fragmentation and collapse. (2)The influencing factors of bedding separation of roadways with extra-thick coal seam are classified to three major groups and a total of fifteen minor classes. Fifty numerical simulation schemes are constructed based on these factors, and the final six key influencing factors are obtained. (3) A "dual-zone" roof control system is proposed. This system adopts high-strength bolts and cables as core components to form stable supporting structures in shallow and deep roof respectively. (4) Four major indicators of roof support safety are addressed to evaluate the roof safety of the supported roadway with extra-thick coal seam, and then a set of evaluation system for roof safety is developed. (5) A typical example adopted the proposed prevention and control system to roof caving disaster of the roadway with extra-thick coal seam is introduced in detail.