This paper investigated the fracture development and deformation of the surrounding rock around the roadway at the Kouzidong coal mine, where fractures were observed and monitored using borehole imaging at different locations. The global-local model was originally used for the prediction of the stresses in hard rock mine, and it has been widely used in solving rock mechanics problems. To overcome the shortcomings of the coupling calculation, this paper implements the global-local simulation model. When simulating multiple rock layers, the numerical results are not well aligned with field observations. However, the combination of the two models is achieved by the displacement boundary conditions, where macroproperties of the material in both DEM and FEM have to be similar. This coupling calculation technique not only is more representative of the mechanical properties of nonlinear rock materials but also considerably reduces the model computation time. With the development of numerical simulation theory, the technique of coupling simulation between the discrete element model (DEM) and the finite element model (FEM) has been used. They found that a roadway driven at a large angle (75°–90°) with respect to the maximum horizontal stress suffers significantly more fracturing than that driven at a small angle (0–15°). Gao and Stead used the discrete element model (DEM) to analyze the relationship between the major principal stress orientation and fracture distribution.
They found that the crack opening and the separation characteristic of this type of roadway are a dynamic process gradually developing upwards. used borehole imaging, geological radar, roof separation monitoring, and other means to study the fracture development process of the roadway roof.
To effectively study the fracture propagation around the soft rock roadway, a series of methods have been suggested, including field surveys, physical similarity modeling, and numerical simulations. To enhance the knowledge on the fracture distribution around the roadway and optimize the supporting design, it is pivotal to understand the crack development and distribution of the surrounding rock around the roadway.
The deformation of the surrounding rock is mainly due to the stress-induced fracture and expansion. Compared with mining at shallow depth, the failure mechanism and mechanical properties of the surrounding rock around roadway are different at deep mining locations, where the large deformation and rheological phenomenon frequently occur. The mechanical behavior of the rock mass is closely related to the mining method as the mining-induced stress redistribution can significantly influence the surrounding rock mass. Introductionĭue to the extensive exploitation of coal, available resources at shallow depth quickly diminish and mining activities below 1000 meters have gradually gained popularity. The deep shear failure also induced the formation of the nonadjacent crushing zone and elastic zone, which is in line with the borehole imaging results. Due to the extensive tensile cracks in the shallow section, the surrounding rock experienced expansion and fracture. From numerical results, it can be seen that the stress concentration at the ribs was released, which led to shear failure at the roof and floor. However, the failure mechanism transformed to shear failure. During longwall retreatment, fractures continuously developed toward the deeper soft rock layer. In the roadway excavation process, fractures were first formed in the shallow section of the roadway and progressively propagated toward the deeper soft rock layer the main failure mechanism was a tensile failure. To effectively study the fracture propagation and distribution of the roadway under longwall retreatment and roadway excavation, the global-local numerical technique was applied via FLAC3D and PFC2D. By analyzing the C value of the fractures in the borehole images,we found that the fracture interval distribution of the surrounding rock of the tunnel, the number of fractures will fluctuate decrease with the increase of the depth. Based on the borehole imaging technique, we found an asymmetric distribution of the fracture zone in the surrounding rock of the roadway. In this paper, both field investigation and numerical simulation were taken to study the fracture evolution and rock deformation of a coal mine roadway at Kouzidong mine, Fuyang, Anhui Province, China. The fracture development and distribution around the deep soft rock roadway are pivotal to any underground design.