Study on compound disaster of rock burst and roof falling in coal mines

With the development of coal mine to the deeper zone,the dynamic disaster of coal mines not only shows some characteristics of rock burst,but also shows some characteristics of roof falling.The two typical disasters break the previous cognitive law that the occurrence of roof fall and rock burst is mutually converse.These two type of disasters are mutually induced and compounded in deep coal roadway with high stress,especially coal roadway with thick top coal.On the basis of summarizing the characteristics of roof (top coal) accidents caused by rock burst of typical roadways in Shandong,Shanxi and Xinjiang mining areas,the concept,mechanism and classification of the compound disaster of rock burst and roof fall in deep roadway were proposed.It is pointed out that the key point of compound disaster mechanism is to reveal the stability principle of the whole roadway system,the subsystem of the fracture area and their interaction.In this paper,the mechanical model of compound disaster in roadway was established.According to the criterion of disturbance response instability,the critical load,the radius of critical softening zone and maximum allowable disturbance stress increment were obtained,the main control factors of the disaster were clarified and the influence of rock burst tendency index,support strength,roadway radius and uniaxial compressive strength on the occurrence of the disaster was analyzed.In addition,the development law of the surrounding rock softening and fracture depth along the increase of the ground stress was clarified.The results show that the main body of dynamic instability of roadway is an unstable system composed of elastic zone,softening zone and fracture zone,and the main body of falling is fracture area.The stable fracture area increases the critical value of rock burst start up,which makes it more difficult to start,but the development of fracture area is easy to cause roof fall.Roadway stability support is the key to solve the compound disaster.Scientific and reasonable support can not only effectively control the surrounding rock fracture and roof falling resistant,but also improve the critical value of rock burst start up.The occurrence mechanism of the compound disaster of rock burst and roof fall is revealed with theoretical study,and the significance of the softening and fracture area and its stability control for the prevention and control of the dynamic disaster in the deep roadway is clarified.