Moisture is one of the most important factors that influences coal seepage and coal-bed methane (CBM) extraction.

The unfavorable factors of underground coal such as dark light, uneven illumination, band shadowing greatly make it difficult to recognize the coal rock at the mining workface accurately. To solve this problem, this paper proposes the fuse attention mechanism ’ s coal rock full-scale network (FAM-CRFSN) model. The deep extraction of coal rock semantic features is achieved by a multi-channel residual attention mechanism and a full-scale connection structure. Meanwhile, the balance between “deep” stacking and error back propagation is achieved by structures such as dilated convolution and Res2Block. Besides, a multi-dimensional loss function consisting of the cross-entropy loss, intersection over union, and multiscale structure similarity loss with pixel-level, area-level, and image-level expressions is established. Finally, the performance of the FAM-CRFSN network is tested with RGB coal rock images collected from an underground coal mining workface and superimposed with different proportions of gaussian noise and salt & pepper noise. The experimental results show that the FAM-CRFSN model can segment the coal rock regions accurately; at a noise intensity of 0.09, it achieves an MIOU of 85.77% and an MPA of 92.12%. Also, it achieves better accuracy and generalization performance than the mainstream semantic segmentation models. This study provides an important theoretical basis for promotes the unmanned and intelligent mining workface.

Coal contains a large number of fractures, whose characteristics are difficult to describe in detail, while their spatial distribution patterns may follow some macroscopic statistical laws. In this paper, several fracture geometric parameters (FGPs) were used to describe a fracture, and the coal seam was represented by a two-dimensional stochastic fracture network (SFN) which was generated and processed through a series of methods in MATLAB. Then, the processed SFN image was able to be imported into COMSOL Multiphysics and converted to a computational domain through the image function. In this way, the influences of different FGPs and their distribution patterns on the permeability of the coal seam were studied, and a finite element model to investigate gas flow properties in the coal seam was carried out. The results show that the permeability of the coal seam increased with the rising of fracture density, length, aperture, and with the decrease of the angle between the fracture orientation and the gas pressure gradient. It has also been found that large-sized fractures have a more significant contribution to coal reservoir permeability. Additionally, a numerical simulation of CBM extraction was carried out to show the potential of the proposed approach in the application of tackling practical engineering problems. According to the results, not only the connectivity of fractures but also variations of gas pressure and velocity can be displayed explicitly, which is consistent well with the actual situation.

It is known that the presence of microstructures in solids such as joints and interfaces has an essential influence on the studies of the development of advanced materials, rock mechanics, civil engineering, and so on. However, microstructures are often neglected in the classical local (Cauchy) continuum model, resulting in inaccurate descriptions of the behavior of microstructured materials. In this work, in order to show the impact of microstructures, an implicit ‘non-local’ model, i.e., micropolar continuum (Cosserat), is used to numerically investigate the effects of direction and scale of microstructures on the tension problem of a composite plate with a circular hole. The results show that distributions of field variables (such as displacements and stresses) have an obvious directionality with respect to the microstructures’ direction. As the scale of microstructures increases, such a direction effect becomes more evident. Unlike the isotropic material where stress concentration occurs at the vertex of the hole and the stress concentration factor is close to 3, for the microstructured composite, the stress concentration can be observed at any location depending on the microstructures’ directions, and the concentration factor can exceed 3 to a maximum close to 9 as the increasing scale of microstructures. In addition, differences in the mechanical behavior between Cosserat and Cauchy models can be also observed; such differences are more evident for the material showing a pronounced orthotropic nature.