Abstract
The fracture development and distribution around the deep soft rock roadway are pivotal to any underground design. 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. Based on the borehole imaging technique, we found an asymmetric distribution of the fracture zone in the surrounding rock of the roadway. 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. 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. 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. During longwall retreatment, fractures continuously developed toward the deeper soft rock layer. However, the failure mechanism transformed to shear failure. 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. Due to the extensive tensile cracks in the shallow section, the surrounding rock experienced expansion and fracture. 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.
Highlights
Due to the extensive exploitation of coal, available resources at shallow depth quickly diminish and mining activities below 1000 meters have gradually gained popularity [1]. e 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 [2]
It has been approved that the roadway instability is directly related to the fracture development in the surrounding rock. rough PFC23, the generation and development of cracks in the roadway excavation and longwall retreatment can be well studied
The mechanism of crack initiation and development under the influence of dynamic pressure in deep soft rock roadway are studied. e 121304 longwall face at Kouzidong coal mine has a typical deep soft rock roadway, which was under the impact of the roadway excavation and the longwall retreatment
Summary
Due to the extensive exploitation of coal, available resources at shallow depth quickly diminish and mining activities below 1000 meters have gradually gained popularity [1]. e 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 [2]. 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 [3]. To effectively study the fracture propagation around the soft rock roadway, a series of methods have been suggested, including field surveys [4], physical similarity modeling [5], and numerical simulations [6, 7]. Is 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. Based on the collected field data, a numerical simulation via PFC was carried out to further investigate the failure mode and rock deformation around the roadway. Limited figures may be included only if they are truly introductory and contain no new results
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