Abstract
The deformation and failure of coal and rock materials is the primary cause of many engineering disasters. How to accurately and effectively monitor and forecast the damage evolution process of coal and rock mass, and form a set of prediction methods and prediction indicators is an urgent engineering problems to be solved in the field of rock mechanics and engineering. As a form of energy dissipation in the deformation process of coal and rock, microseismic (MS) can indirectly reflect the damage of coal and rock. In order to analyze the relationship between the damage degree of coal and rock and time-frequency characteristics of MS, the deformation and fracture process of coal and rock materials under different loading modes was tested. The time-frequency characteristics and generation mechanism of MS were analyzed under different loading stages. Meanwhile, the influences of properties of coal and rock materials on MS signals were studied. Results show that there is an evident mode cutoff point between high-frequency and low-frequency MS signals. The properties of coal and rock, such as the development degree of the original fracture, particle size and dense degree have a decisive influence on the amplitude, frequency, energy and other characteristic parameters of MS signals. The change of MS parameters is closely related to material damage, but has no strong relation with the loading rate. The richness of MS signals before the main fracture depends on the homogeneity of materials. With the increase of damage, the energy release rate increases, which can lead to the widening of MS signals spectrum. The stiffness and natural frequency of specimens decreases correspondingly. Meanwhile, the main reason that the dominant frequency of MS detected by sensors installed on the surface of coal and rock materials is mainly low-frequency is friction loss and the resonance effect. In addition, the spectrum and energy evolution of MS can be used as a characterization method of the damage degree of coal and rock materials. Furthermore, the results can provide important reference for prediction and early warning of some rock engineering disasters.
Highlights
Many countries and regions in the world have reduced the use of coal, some countries, e.g., China, India and South Africa, remain heavily dependent on coal resources
Coal and rock materials are under long-term
The results showed that MS activities generally have time priority and spatial consistency to rock burst events, which could provide a basis for rock burst prediction of tunnel and microseismic monitoring and early warnings
Summary
Many countries and regions in the world have reduced the use of coal, some countries, e.g., China, India and South Africa, remain heavily dependent on coal resources. Coal consumption still accounts for a large proportion in the energy consumption structure in these countries. With the depletion of shallow coal resources, especially in China, mining depth of a coal mine increases sharply, and high ground stress, high ground temperature, hyperosmosis and strong disturbance problems are gradually emerging. The normal mining disturbance is easy to induce the deformation and fracture of coal or rock materials and cause serious hazards, such as rock burst, coal and gas outburst and large deformation of surrounding rock [1,2]. Influenced by environmental protection and policy orientation, the proportion of oil, natural gas and new energy in the disposable energy structure has increased. The study on the damage of coal and rock in the development of these resources should be getting enough concern
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