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As a research hotspot, pillarless coal mining technology has a high resource recovery rate and low roadway surrounding rock stress. To grasp the three-dimensional fracture characteristics of the basic roof is the basic to reveal the strata behavior mechanism in the pillarless working face. Thus, aiming at pillarless coal mining, the analytical solu...
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... summary, the small deflection theory of elastic thin plates can be applied to build the fracture mechanics model for a basic roof. Figure 2 shows the succession sequence of pillarless working faces. During the advance of the first working face, the roadway next to the succeeding working face will be retained by the roof-cutting method, and then this roof-cutting roadway will serve the second stope face. ...
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... As such, four methods have been developed: three-dimensional similarity simulation, three-dimensional numerical simulation, on-site measurement, and three-dimensional plate theory, to explore the roof fracture morphology and movement laws. For three-dimensional physical similarity simulation, experiments have identified that a basic roof, a type of hard roof, exhibits an 'O-X'-shaped break (Guo et al. 2021). A specially designed large-scale experimental platform further revealed periodic 'C-Y'-shaped breaks in high-level key layers (Zhu et al. 2017). ...
Hard roof’s 3D breaking characteristics is vital for mining pressure control. However, the research concerning a longwall face that employs an innovative roof-cutting technology via a chainsaw arm machine (RCTCAM) is scant. To address this gap, this paper thoroughly analyzes RCTCAM’s core equipment and roof-cutting procedures. Firstly, the thin elastic plate theory and the superposition principle were applied to establish the first and periodic break mechanical models of hard roofs using the RCTCAM. These mechanical models elucidated the distribution laws of the first and third principal bending moments in a hard roof. Following this, based on tensile failure criteria and crack expansion criteria, the study uncovered that the hard roof's first break transitioned from an ‘O–X’ shape to a ‘U–Y’ shape, while its periodic break morphed from a ‘C–ン’ shape to an ‘L–ノ’ shape. This transformation led to a unique phenomenon. The rotation of arc-shaped triangular plates formed during the 'O–X' and ‘C–ン’ -shaped breaks resulted in severe damage to a gob-side roadway. However, a longwall face employing the RCTCAM did not produce such plates, effectively avoiding the associated damage. By implementing the RCTCAM in Workface 8311 of the Yanya Mine in China, the stress peaks of the coal pillars were reduced on average by 22.8%, and the deformation of the roadway decreased by 27.8%. These findings underline the success of the RCTCAM in achieving pressure relief for a gob-side roadway.
... Guo et al. [10] analyzed and studied the stability of mining-induced overburden structures under a load of new buildings, and they established a mechanical model adapted to the engineering background to analyze the rationality of the stability criterion of the overburden strata. Guo et al. [11] used the elastic sheet theory to analyze the analytical solution of the three-dimensional fracture mechanics model of the basic roof for mining without a coal pillar. The fracture characteristics of the main roof cut by continuous and discontinuous artificial cracks are analyzed. ...
The water inrush from the roof of the coal mine is closely related to the movement failure of overburdened rock and the height of the water-conducting fracture zone. In this work, based on the research background of water disaster prevention and control of the No. 2 coal seam roofs in Jinxinda Coal Mine, the stability characteristics of overlying rock in the working face are analyzed through combining theoretical analysis and numerical simulation. According to the theory of key strata, the fracture conditions of hard rock and soft rock are analyzed, and the maximum height of the water-conducting fracture zone in the 201 working face is calculated to be 35.72 m. The crack evolution law of composite roofs was simulated and analyzed using discrete element software. It was found that the basic roof (4.50 m thick) and the fine sandstone (7.64 m thick) are the two inferior key strata, and the maximum development height of the water-conducting crack is 36 m, which is basically consistent with the field measured results. Transient electromagnetic exploration technology was used to detect the working face, and nine abnormal areas were found. In order to prevent the influence of water disasters in abnormal areas during mining, drilling verification is carried out in abnormal areas. According to the analysis of drilling verification, there are no water disasters in the geophysical anomaly area, but the management of the roof after mining should be strengthened during mining. The expected research results not only enrich the rock formation control theory and roof water inrush mechanism; they also have important practical significance in guiding the safety production of a coal mine.
... Prevention and control are the main means to avoid mine geological disasters. It is necessary to select a reasonable mining area (scientific planning), reasonable mining method (scientific mining) and engineering measures (filling mining) (Fan et al. 2017;Guo et al. 2021). Among them, engineering measures are the focus of researchers, because the mining area planning and mining method determination are completed before coal seam mining. ...
The failure form of overburden and surface is an important basis for developing mining damage control and ecological restoration measures. For high-intensity mining, the failure forms were divided into three categories to analyse the breaking law of key strata, the form of structural instability, the development characteristics of water-conducting fractures, and the dynamic evolution process of surface cracks through the UDEC numerical simulation and field observation. The results indicate that the whole cutting of overburden leads to the formation of step-like ground fissures (sinkholes) with large height difference when the surface in the caved zone with single key stratum. The primary key stratum forms the step beam structure and loses stability periodically when the surface in the fracture zone. The distribution of ground fissures is mainly tensile type, supplemented by step-like ground fissures with a relatively small height difference. The primary key stratum fracture incompletely, and forms tensile ground fissures with small width and “self-repaired” when the surface in the sagging zone. Then the effective control measures can be proposed based on the summarized damage level of production safety and ecological environment in high-intensity mining.
... As the excavation of the ore body, the roof, regarded as a thin plate, is subjected to different boundary conditions. The stress distribution and fracture modes will change under different supports 20,21 . Ma et al. 22 considered that pressure arch theory is used to derive the load borne by the goaf roof. ...
In underground mining, the dip angle is one of the widely recognized factors that cause the asymmetric deformation of the goaf/stope roof, but characterizing the degree of asymmetric roof deformation is still a challenge. The goal of this research is to try to solve this problem with a theoretical model and numerical method. In an inclined ore seam, the mining load produces both normal and tangential effects on the inclined roof. A theoretical model was developed employing thin plate theory for enabling describe the asymmetric deformation of the roof caused by inclination. The proposed model describes not only the bending deformation state of the roof but also the deformation characteristics. Subsequently, the law of asymmetric deformation of roofs with varying inclinations was presented by numerical method. Under the same conditions, the numerical results of the asymmetric deformation of the roof are consistent with the theoretical results. Finally, the degree of asymmetrical deformation was characterized and quantified by the distance between the maximum subsidence point and the center of the roof. There exist three modes of asymmetric deformation, which are controlled by both dip angle and in-situ stress ratio. The results show that the shear load caused by dip angle is the root cause of asymmetric deformation of the roof. This study provides a theoretical basis for the asymmetric deformation control of the inclined roof.
The safe and efficient driving of the roadway along the gob is becoming an increasing challenge due to the influence of the integrity and bearing capacity of the side coal and rock mass in the gob under the roof cutting mining mode. The mechanism of protection of the gob-side roadway is shown by modeling the influence of roof cutting and the application of a destress technique on the lateral coal and rock mass zones. The distribution characteristics of stress, displacement, and fracture in the overburden are analyzed by numerical simulation method under the three working conditions. The results indicate (1) construction of row holes and blasting can form artificial structure’s fracture plane above the roadway, which can effectively cut the connection of overburden. The artificial structure’s fracture plane decreases the peak value of the lateral coal body’s support pressure. The peak point and the critical location of the stress reduction area are both transferred to the deep part at the same time, providing adequate space for the gob-side roadway. (2) The stress arch foot in the lateral rock mass rises to the rock layer at the bottom of the roof cutting plane after top cutting, as does the high-pressure area of deviator stress. The fracture plane prevents lateral coal and rock mass instability and limits the negative effects of roof deformation above the gob-side roadway. (3) The triangle slip fracture zone moves to over the roof cutting drilling zone due to the fracture plane, showing a high position compared to its original zone.
