Abstract
Under the superposed action of the primary rock stress and the mining stress, the compound roof of a roadway will have irregular plastic failure zone with greater depth, resulting in a wide range of non-uniform deformations and roof failures. Mastering the deformation and failure characteristics of this roof is essentially to recognize the development of the plastic zone of a compound roof. In this paper, the on-site roof detection method is mainly adopted to arrange a large number of boreholes for visualization and the deep displacement monitoring with the high-density points. Combined with numerical simulations, the rupture development characteristics and deformation mechanisms of the compound roof are revealed. The results show that the magnitude and direction of the principal stress of surrounding rock in a mining roadway are constantly changing, and the penetrating phenomenon will occur during the plastic zone expansion process. The order of the compound roof rupture as follows: shallow strata plastic failure, deep strata penetrating plastic failure and middle strata rupture. Severe roof deformation is mainly caused by plastic failure, and the strong deformation pressure caused by deep strata penetration plastic failure can easily lead to tensile failure and rupture in the middle strata. According to the plastic zone penetration development of the compound roof, the hierarchical support design led by the long-extension bolt is carried out on the test roadway. The monitoring results show that the roof is controlled well. The research results can provide a reference for the control of compound roofs in mining roadways.
Highlights
The plastic failure of roadway roofs is an important reason for the overall rupture of the roofs, the large deformation of the surrounding rock, and the failure of supports which can lead to roof collapse
The support design is usually based on the geometry of the plastic zone of the surrounding rock [1,2,3,4]
It is found that the roadway-surrounding rock is in a highly deviated stress environment because of the influence of mining and the surrounding rock plastic zone will have a dangerous expansion, roof stability is seriously affected, the plastic zone’s shape is no longer a circular, elliptical and other regular shape as in traditional theory [5,6,7,8]
Summary
The plastic failure of roadway roofs is an important reason for the overall rupture of the roofs, the large deformation of the surrounding rock, and the failure of supports which can lead to roof collapse. Revealing the development of the plastic zone in the compound roof during the mining process has practical significance for design of the roof support parameters, the choice of supporting time and the identification of hidden roof fall dangers. Many scholars have proposed a targeted roof control technology and disaster warning method by analyzing the failure mechanisms of mining roadway roof He et al [27,28,29] used the material point method (MPM) to simulate the large deformation and failure process of deep rocks, and proposed the support idea of large deformation roadway under the influence of mining. Gu et al [30,31] measured the failure characteristics of the surrounding rocks on the mining roadway roof by using a strata detector, and investigated the occurrence mechanism of roof-fall and the related supporting control method in detail. The research results provide reference for the roof fall control and support parameter design of compound roof in mining roadway
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