Limit Analysis of Roof Falling in Roadway with Water-Rich Surrounding Rock

In this paper, a roof falling and failure mechanism of roadway with water-rich surrounding rock is deduced based on upper bound method of plastic mechanics and variational principle. For the derivation, a roof falling structure of the roadway is constructed according to the characteristics of the roadway; and it is also based on Hoek–Brown strength criterion and its associated flow rules. The structure is made with the consideration of the influence from stress level on roof rock, formation water pressure and supporting load. A typical roadway with water-rich surrounding rock is taken as an example of field practice to analyze the influence of different mechanical parameters on roof failure mechanism. The roadway is located in Guotun Coal Mine, which is over a 1000 m deep. The calculation results of this study show the size of falling piece from roof represents the safety performance of roof; the size will be enlarged along with the increase of empirical parameter A, tensile strength, compressive strength and supporting load of rock; and meanwhile the size will be reduced along with the increase of empirical parameter B, stress and weight of rock. Among all the factors, tensile strength of rock and stress level of roof rock have a significant effect on roof failure mechanism; parameter B determines the fracture shape of the falling piece from roof; and the fracture curvature of the falling piece decreases with the increase of the parameter B.