Study on the stability of roof beam consisted of cracked rock

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This research is one of the fundamental study to clarify the failure mechanism of tunnel roof, which is a problem in coal mine in the world.Recently, the system rock bolt becomes a main support member of the tunnel. However, a large scale fracture of the roof occurred in a coal mine in United Kingdom a few years ago. A cause of this accident is considered to be too much confidence in the ability of the system rock bolt. Therefore, it is necessary to develop the procedure to predict the fracture of roof beam. There are many theoretical and experimental researches until now. However, the theory of rock beam has hot been constructed. This cause is considered to be the difficulty to introduce the complex problem, which is opening and closing of the preexist joints in a rock beam, initiation and propagation of the cracks, in the theory of rock beam.In this research, the behavior of roof beam of cracked rock is analyzed, based on the rock mechanics. The obtained results are as follows :1) The cause of fracture of the roof beam is classified into the following three classes. First is the lack of the frictional force on the support plane of the roof beam. Second is the buckling of the roof beam. Third is the compressive fracture of rock near the support plane of the roof beam.2) It is made clear that the criterion on the buckling of the roof beam is represented by the maximum displacement and its location induced.3) To analysis behavior of the roof beam due to the compressive fracture of rock near the support plane, the no-tension model is suggested. Using the model which is assumed that the tensile strength of rock parallel to the beam axis is zero, the results of the analysis are good agreement with those of the experiment.4) It is concluded that the ratio of the Young's modulus to the uniaxial compressive strength is an important parameter to estimate the stability on the roof beam consisted of cracked rock.