Analysis and Optimization of Entry Stability in Underground Longwall Mining

Abstract

For sustainable utilization of limited coal resources, it is important to increase the coal recovery rate and reduce mine accidents, especially those occurring in the entry (gateroad). Entry stabilities are vital for ventilation, transportation and other essential services in underground coal mining. In the present study, a finite difference model was built to investigate stress evolutions around the entry, and true triaxial tests were carried out at the laboratory to explore entry wall stabilities under different mining conditions. The modeling and experimental results indicated that a wide coal pillar was favorable for entry stabilities, but oversize pillars caused a serious waste of coal resources. As the width of the entry wall decreased, the integrated vertical stress, induced by two adjacent mining panels, coupled with each other and experienced an increase on the entry wall, which inevitably weakened the stability of the entry. Therefore, mining with coal pillars always involves a tradeoff between economy and safety. To address this problem, an innovative non-pillar mining technique by optimizing the entry surrounding structures was proposed. Numerical simulation showed that the deformation of the entry roof decreased by approximately 66% after adopting the new approach, compared with that using the conventional mining method. Field monitoring indicated that the stress condition of the entry was significantly improved and the average roof pressure decreased by appropriately 60.33% after adopting the new technique. This work provides an economical and effective approach to achieve sustainable exploitation of underground coal resources.

Roof Deformation Characteristics and Preventive Techniques Using a Novel Non-Pillar Mining Method of Gob-Side Entry Retaining by Roof Cutting

“…Compared with GER, this mining technology has more prominent advantages, such as reducing the cost of mining, weakening the local stress concentration in roadway surrounding rocks, and preventing uneven settlement of the earth's surface. When the working face (F1) is mined with GERRC, the roadway R1 is not excavated ahead of the working face but is formed and retained behind the working face by using technologies including directional roof cutting, support with constant resistance large deformation cable (CRLDC), temporary support, and a series of equipment [20][21][22][23]. After F1 is finished, the recovery equipment can be immediately moved to F2 using shield haulers.…”

Finite Element Analysis of the State of Stresses on the Structures of Buildings Influenced by Underground Mining of Hard Coal Seams in the Jiu Valley Basin (Romania)

“…The elastic modulus, cohesion, and tensile strength results are generally 0.1-0.25 of the laboratory testing results. The Poisson's ratios are approximately 1:2-1:4 of the laboratory testing results [51]. For the materials used in the structural elements of the structures modelled with finite element method, a series of equivalent average properties were adopted, both for reinforced concrete and for the masonry walls (zigzag bricks and mortar [23]), shown in Table 4.…”

Nonlinear Large Deformation Mechanism and Stability Control of Deep Soft Rock Roadway: A Case Study in China

“…The application shows that the coupling support countermeasure can effectively reduce the nonlinear large deformation of the surrounding rock and help to maintain the stability of the deep soft rock roadway at Xin'an coal mine.Sustainability 2019, 11, 6243 2 of 20 nonlinear mechanical phenomena become more and more intense in the deep soft rock roadways [4][5][6]. A series of nonlinear large deformation of surrounding rocks, such as roof sinking, shrinkage, floor heave, roof caving, rock burst, and ground burst have appeared in roadways [7][8][9]. The support mechanism and control countermeasure adopted in shallow mining have some limitations, which cannot fully adapt to deep mining activities.…”