Study on the stability of roof beam consisted of cracked rock

本研究是阐明巷道顶板破坏机理的基础性研究之一，是目前国内外煤矿普遍存在的一大难题。然而，几年前，英国一座煤矿发生了大规模的顶板断裂。这起事故的原因被认为是对系统锚杆的能力过于自信。因此，有必要开发预测顶板梁断裂的程序。到目前为止，已有大量的理论和实验研究。然而，岩梁理论的构建一直很火热。这一原因被认为是岩梁理论中难以引入的复杂问题，即岩梁中预先存在的节理的张开和闭合、裂纹的萌生和扩展。研究结果如下：1)顶梁断裂原因分为以下三类。首先是屋面梁支撑面的摩擦力不足。二是屋面梁的屈曲问题。三是顶梁支撑面附近岩石的压缩断裂。2)明确了顶梁屈曲的判据是由引起的最大位移及其位置来表示的。3)为了分析顶梁在支撑面附近岩石压缩断裂时的行为，提出了无拉伸模型。采用假定岩石平行于梁轴线的抗拉强度为零的模型，分析结果与试验结果吻合较好。4)得出杨氏弹性模数与单轴抗压强度之比是评价含裂隙岩石顶板梁稳定性的重要参数。

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.