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Numerical simulation on effect of coal pillar width on stability of retained roadway: A case study of Khe Cham Coal Mine, Vietnam

Le Quang Phuc, Le Tien Dung

Journal of Sustainable Mining

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2024

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Vol. 23, iss. 1

1--9

EN

When extracting coal seams in Vietnam underground mines, coal pillars are often left unmined for the protection of retained roadways in the longwall mining method. During longwall mining operations, coal pillars are often placed where high-stress concentrations occur in the abutment pressure zone of adjacent panels, especially when extracting seams under hard-to-cave main roof conditions. The instability of coal pillars under the loading of the main roof may cause the roadway to collapse, threatening the safe operation of a coal mine. This paper presents a detailed numerical investigation of the effect of coal pillar width on the stability of retained roadway under hard-to-cave main roof conditions, which has not been fully understood in previous studies. The results indicate that as the width of the coal pillar increases, the peak stress gradually moves from the virgin coal side to the pillar side, and an elastic zone will gradually be formed in the center of the pillar. A pillar width of less than 40 m coal pillars is easily destroyed under the great pressure caused by the hard main roof. A pillar width greater than 40 m creates a safe condition and has enough bearing capacity to maintain the stability of retained roadways. Based on these results, this paper proposes to use an improved longwall mining method where the coal pillars should be mined together with the adjacent panel to reduce coal loss in pillars.

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Fracture Mechanism of Hard Main Roof and Determining the Width of Coal Pillars when Extracting Flat-lying Coal Seams

Le Quang Phuc, Dao Van Chi, Nguyen Phi Hung, Vu Thai Tien Dung

Inżynieria Mineralna

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2023

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no. 2, vol. 1

271--280

EN

In underground coal mining, the stability of roadways and gob-side entry depends on the coal pillar width. An unreasonable width of the coal pillar will cause the roadway to be in a dangerous zone of influence of the abutment pressure, leading to severe roadway deformation. This paper studies the fracture mechanism of the hard main roof and reasonable coal pillar width to protect the stability of gob-side entry driving. The research results show that when mining a coal seam under a hard main roof, the console of the main roof on the edge of the coal seam has the form of hinge structure. The great load of the roof layers and the rotation of the console are the main causes leading to the variation of the stress field in the coal seam. According to the development law of the stress field, after the main roof completes the collapse process, the peak of the maximum stress will move deep into the solid coal seam, and on the edge of the coal seam it will form a low-stress zone. Research results from the case of Seam #11 of Khe Cham coal mine, Vietnam show that the gob-side entry will be well stabilized when the narrow coal pillar between it and the boundary of the gob is 4–5 m.

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Cause and Solution to Roadway Deformation in Vietnam Underground Coal Mine

Le Quang Phuc

Inżynieria Mineralna

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2021

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no. 2

381--390

EN

The deformation and support method of roadways have always been important issues in safe mining and production. Vinacomin's statistics show that, by 2021, there will be 64.19 km of roadways that need to be repaired (accounting for 25% of the total new roadways). Thus, the problem of maintaining roadway stability is facing difficulties in underground coal mines in Vietnam. To find out the causes of roadway failures, a case study at roadways of the Khe Cham I and Khe Cham III coal mines, Vietnam, is presented in this paper. Based on the results of a detailed field survey, the deformation characteristics of roadways and the failure mode of support structures were investigated. The results show that the roadway deformation is severe and the main support cannot control surrounding rock mass. Also, the destruction of support structure is frequent on reused roadways, affecting production efficiency and work safety. Therefore, to reduce deformation and increase roadway stability, a new support method called “multistage anchor of rock bolt + cable bolt” has been developed and a new longwall mining system with critical coal pillar width has been proposed. The new findings of the research can provide references for scientific studies, and apply them in Vietnam's underground coal mine practices.

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Improvement of the Loading Capacity of Narrow Coal Pillars and Control Roadway Deformation in the Longwall Mining System. A Case Study at Khe Cham Coal Mine (Vietnam)

Le Quang Phuc, Zubov V. P., Phung Manh Dac

Inżynieria Mineralna

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2020

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no. 2, vol. 1

115--122

EN

Currently, the application of coal pillars to protect an adjacent roadway is a common method in Vietnam when exploiting according to the longwall system. Therefore, the width of a coal pillar is an important issue for the stability of a roadway. In order to reduce coal loss in these coal pillars, they tend to be designed in a narrow coal pillar style but still have to ensure that the adjacent roadway can meet safe coal production conditions. The stability of roadways and coal pillars is related to many factors such as technical mechanical characteristics, physical and mechanical properties of coal, stress environment and support methods. The bearing structure of the coal pillar and the around rock a roadway is analyzed and it has been shown that enhancing roadway support and improving the carrying capacity of coal pillars can control the deformation of the surrounding rock. A study related to the stability and safety of roadways and small coal pillars in the longwall mining system has been carried out. Stabilization factors have been considered, especially the state of stress in the coal pillars and the deformation of the roadway. By applying the numerical simulation method, the stress of the coal pillar and the deformation of the adjacent roadway under different supporting solutions were analyzed and evaluated. By using this method, the rock bolt roadway support solution combined with the long cable bolt in the roadway roof and the coal pillar was selected in the safe condition of the mining process. Because cable bolt can improve the flexibility of the coal pillar such as: reducing the size of the plastic area on both sides of the pillar; enhancing coal pillar stability in the core area by providing great drag and tensile for coal pillars; contributing to improving the anchor point fixation of rock bolt. The conclusions obtained may provide a certain reference parameters to improve mining efficiency and labor safety in underground coal mines.

PL

Obecnie stosowanie filarów węglowych do ochrony sąsiednich wyrobisk złożowych jest powszechną metodą przy eksploatacji systemem ścianowym w Wietnamie. Wymiary filarów jest istotną kwestią dla stabilności wyrobisk złożowych. Aby zmniejszyć straty węgla, zwykle są one projektowane w stylu wąskich filarów, ale nadal muszą zapewniać, że sąsiednie wyrobiska muszą spełniać bezpieczne warunki. Stateczność wyrobisk i filarów węglowych jest związana z wieloma czynnikami, takimi jak techniczne właściwości fizyczno-mechaniczne górotworu, naprężenia i metody podparcia. Przeanalizowano konstrukcję nośną filara węglowego i skały otaczającej chodniki wykazano, że wzmocnienie podparcia wyrobisk i polepszenie nośności filarów węglowych może kontrolować odkształcenia otaczającej skały. W artykule, przedstawiono wyniki badania dotyczącego stateczności wyrobisk i małych filarów w ścianowym systemie. Uwzględniono czynniki stabilizujące, w szczególności stan naprężeń w filarach oraz odkształcenie chodników. Wykorzystując metodę symulacji numerycznej, przeanalizowano i oceniono naprężenie w filarach węglowych oraz odkształcenie sąsiednich chodników przy różnych rozwiązaniach podporowych. Ponieważ śruba linowa może poprawić elastyczność filarów, na przykład: zmniejszenie rozmiaru obszaru z tworzywa sztucznego po obu stronach filara; zwiększenie stabilności filara węglowego w obszarze rdzeniowym poprzez zapewnienie dużego oporu i rozciągliwości filarów; przyczynianie się do poprawy mocowania punktu kotwienia śruby do skał. Uzyskane wnioski mogą dostarczyć rozwiązania dla poprawy efektywności wydobycia i bezpieczeństwa pracy w podziemnych kopalniach węgla kamiennego.