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Single fracture is the most basic element in complex fracture network of rock mass. Therefore, the study of flow characteristics of single fracture is an important way to reasonably predict the complex flow state in engineering rock mass. In order to study the flow characteristics of fractal single fracture, fracture models with dif?ferent fractal dimension and different fracture width are established in this paper. The results show that: the blocking effect of rough structure on fluid is obviously enhanced under high pressure. In addition, it is weakened and reaches a steady-state with the increase of fracture fractal dimension. The larger the fracture width is, the more obvious the phenomenon is. The hydraulic gradient index tends to 0.5 with the increase of fracture width when fractal dimension is greater than 1.3. It also could tend to 0.5 with the increase of fractal dimension when fracture width is greater than 1 mm.

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Gas has been one of the main causes of coal mine safety accidents. At present, the most commonly used treatment method is still gas drainage in advance. The permeability of coal seams is the most important factor affecting gas drainage. According to the coal density, P-wave velocity and fracture distribution, the coal samples are grouped to eliminate the influence of the differences of the coal samples on the experimental results. The results show that due to the decrease of samples integrity and the increase of gas osmotic pressure, the peak strength of the sample will reduce, and eventually the stable permeability will increase. Besides, the starting point of permeability will also appear earlier (relative to the peak intensity point of the samples). It is worth noting that the starting point of the sample permeability is highly consistent with the expansion point of sample volume. As the loading and unloading rate increases, the peak strength of the samples will first decrease and then increase. Similarly, the final stable permeability of the samples also shows a trend of first decreasing and then increasing.