“…Assuming that the lateral action of coal seam floor and mining front has water pressure at this time, the micro-element is taken for stress analysis, and the stress is balanced in the vertical and horizontal directions. The stress analysis of the element is carried out as 21 : Figure 24 Stress analysis model of plastic zone of waterproof coal pillar. …”
Section: Discussionmentioning
confidence: 99%
“…The methods dealing with mine construction can be modified to limit this potential danger, such as dewatering, advanced drilling support, rock grouting, and the waterproof coal pillar setting 19 , 20 . In the above-mentioned measures, the reasonable waterproof coal pillar is considered an economical and efficient mean to prevent water inrush 21 , 22 . Several formulas pertaining to the strength and width of the waterproof coal pillar are proposed by scholars 23 – 25 .…”
Numerous field examples of coal seam mining show that when coal seams under confined water are mined close to faults, water inrush effects on complex mining surfaces occur. Obeying similarity rules, physical similarity models consisting of sand, lime, and plaster were used to investigate the water conducting process, along with stress and displacement measured by a combination of mechanical senor, total station, and video camera-. Comparing the physical model tests with the calculation results of elastoplastic limit equilibrium theory, the rationality of the model has been verified. Besides, a safe width of the waterproof coal pillar has been obtained. It can be demonstrated from the model observations that the coal seam in front of the mining can be divided into three areas with different characteristics of stress and displacement, namely, which are the fault-affected area, the elastic area, and the plastic yield crack area. A closed-loop water inlet and outlet pipeline composed of a water control platform that can provide stable water pressure, and water bags pre-buried in the fault was used to simulate the water conduction in the fracture zone. Integrate the development law of stress, displacement, and water conduction coming from the upper and lower walls of the fault to further determine the reasonable width of the waterproof coal pillar.
“…Assuming that the lateral action of coal seam floor and mining front has water pressure at this time, the micro-element is taken for stress analysis, and the stress is balanced in the vertical and horizontal directions. The stress analysis of the element is carried out as 21 : Figure 24 Stress analysis model of plastic zone of waterproof coal pillar. …”
Section: Discussionmentioning
confidence: 99%
“…The methods dealing with mine construction can be modified to limit this potential danger, such as dewatering, advanced drilling support, rock grouting, and the waterproof coal pillar setting 19 , 20 . In the above-mentioned measures, the reasonable waterproof coal pillar is considered an economical and efficient mean to prevent water inrush 21 , 22 . Several formulas pertaining to the strength and width of the waterproof coal pillar are proposed by scholars 23 – 25 .…”
Numerous field examples of coal seam mining show that when coal seams under confined water are mined close to faults, water inrush effects on complex mining surfaces occur. Obeying similarity rules, physical similarity models consisting of sand, lime, and plaster were used to investigate the water conducting process, along with stress and displacement measured by a combination of mechanical senor, total station, and video camera-. Comparing the physical model tests with the calculation results of elastoplastic limit equilibrium theory, the rationality of the model has been verified. Besides, a safe width of the waterproof coal pillar has been obtained. It can be demonstrated from the model observations that the coal seam in front of the mining can be divided into three areas with different characteristics of stress and displacement, namely, which are the fault-affected area, the elastic area, and the plastic yield crack area. A closed-loop water inlet and outlet pipeline composed of a water control platform that can provide stable water pressure, and water bags pre-buried in the fault was used to simulate the water conduction in the fracture zone. Integrate the development law of stress, displacement, and water conduction coming from the upper and lower walls of the fault to further determine the reasonable width of the waterproof coal pillar.
“…In fact, scholars and engineers have conducted a lot of related research in China. Early exploration, prediction, evaluation of geological conditions and types of water disasters, and methods of prevention and control are the focus of these studies [13][14][15][16][17][18][19][20][21]. All of these effectively reduce the occurrence of water inrush accidents in coal mines.…”
On 22 May 2017, a groundwater inrush accident occurred in the gob area of coal floor at Dongyu Coal Mine in Qingxu County, Shanxi Province, China. The water inrush accident caused great damage, among which six people died and the direct economic loss was about CNY 5.05 million. An elliptical permeable passage appeared at the floor of the water inrush point, and the lithology of the outburst is mainly fragmented sandy mudstone and siltstone of coal roof No.2 in the lower layer of coal seam No.3, which is currently being mined, with a peak inflow of 500 m3/h. The water inrush happened due to following reasons: There is an abandoned stagnant water-closed roadway in coal seam No.2, which is the lower mine group of coal seam No.3. The abandoned roadway of coal seam No.2 is an inclined roadway. The water level of the roadway far away from the accident point is higher than the floor elevation of coal seam No.3. Under the joint action of water pressure, mining disturbance, and weakening of goaf water immersion, the original equilibrium state was broken, resulting in the destruction of the only 7 m water-barrier rock pillar between coal seam No.3 and coal seam No.2. The water in the goaf led upward along the roof crack, gradually evolved from seepage to gushing water, and a large amount of goaf water poured into the roadway in the working face of the 03304 panel, finally leading to the occurrence of catastrophic water inrush. Technically, the miners did not implement the technical provisions of the coal mine water control regulations, leading to the accident. In addition, the failure to arrange evacuees to a safe location after apparent signs of water inrush also increased the catastrophic level of the accident.
“…Because of the different geological and hydrogeological conditions, water inrush accidents rarely happened in some major coal mining countries in the world, such as the USA, Russia, Australia, India, South Africa, Poland, Germany, Canada, and Indonesia [6,7]. In contrast, water inrush accidents often occur in coal mines in China [8]. After more than half a century of mining, the shallow coal resources in China have been exhausted.…”
Retaining a waterproof coal pillar is the most effective water conservation method for a roadway close to the gob, and determining a reasonable width of the waterproof coal pillar has been a common problem among mining scholars for a considerably long time. Based on the mining of the 15208 mining face in Xinjing Coal Mine, the structure of waterproof coal pillar is divided into a mine-pressure-influenced plastic zone, an effective waterproof elastic core zone, and a water pressure failure zone. The mine-pressure-influenced plastic zone width is determined by using the limit equilibrium theory, the parabolic strength theory, and the separation variable method. The effective waterproof elastic core zone width is determined by the semi-inverse solution method, and the water pressure failure zone width is determined by considering the infiltration and softening of water. After that, combined with the previous theoretical analysis of engineering examples, the theoretical value of waterproof coal pillar width is obtained. In addition, the physical shape distribution of the waterproof coal pillar is measured by ultrasonic detection technology. The results are consistent with the field measured results. The correctness of the model is verified. Finally, the rationality of the model is verified by comparing with the previous classical models. The research results are applied to the design of the waterproof coal pillar in Xinjing Coal Mine, which could provide a theoretical basis for determining the width of the waterproof coal pillar located close to a gob.
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