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Gob-side entry retaining (GER) is a popular non-pillar mining technique regarding how to reserve a gateroad for the use of next panel mining. When used in thick coal seams, the conventional entry retaining method requires a huge amount of filling materials and may cause entry (gateroad) accidents. Thus, an innovative non-pillar longwall mining approach is introduced. First, structural and mechanical models were built to explore the mechanism of the new approach. The modeling results indicate that effective bulking of the gob roof and reasonable support of the entry roof were key governing factors in improving entry stabilities and reducing roof deformations. Accordingly, a directional roof fracturing technique was proposed to contribute to gob roof caving, and a constant resistance and large deformation anchor (CRLDA) cable was used to stabilize the entry roof. Subsequently, the evolutionary laws of the roof structure and stresses were explored using numerical simulation. It was found that the structure of the surrounding rocks around the retained entry changed significantly after roof fracturing. The stress-bearing center was transferred to the gob area, and the entry roof was in a low stress environment after adopting the approach. Finally, the approach was tested on a thick coal seam longwall mining panel. Field monitoring indicates that the retained entry was in a stable state and the index of the retained entry met the requirement of the next mining panel. This work provides an effective and economical approach to non-pillar longwall mining in thick coal seams.

Under the condition of the shallow coal seam, the laws of roof activity after large mining height longwall face mining and prevention measures for large-area roof weighting are problems that need to be solved urgently. In the background of the super large mining height working face in the upper 108 working face of Jinjitan Coal Mine 12-2, the spatial distribution characteristics of the development and change of the mining-induced abutment pressure and the related support design in the 8.2 m super large mining height and fully mechanized mining face were conducted. It reveals the distribution characteristics of the dynamic stress field and internal and external stress fields. The influence range of the abutment pressure of the super high mining height working face was measured on site. The numerical simulation is carried out, the roadway support structure is analyzed, and the improvement measures are proposed. The research results demonstrate that: The influence range of abutment pressure is 234 m, the obvious influence range of the leading pressure is 47–60 m, and the peak position of the influence of the leading pressure is 15–20 m. The 5 m range is the lateral inward stress field of the coal pillar, the 10–15 m range is the outward stress field of the coal pillar, and the 20 m range is the original rock stress field of the coal pillar. Therefore, it is proposed that the reasonable size of the coal pillar for roadway protection is 20–22 m. Adjusting the distance between screw steel and FRP bolts from 1000 mm to 1200 mm, the length of the roof prestressed anchor cable should be appropriately reduced to 5.5–6 m according to the lithology of the roof.

For the study of the layout of the roadway in the coal pillar and floor strata co-mining working face at the Zhaogu No.2 mine, a mechanical model of the segmental coal pillar within the working face was established through theoretical calculations. The analysis considered the stress state of the coal pillar area under different collapse conditions in the goaf after upper strata mining. Additionally, FLAC 3D numerical simulation software was used to simulate the stress distribution in the roadway for different layout positions during strata mining, thereby clarifying the impact of working face mining on the side roadway of the segmental coal pillar. The results show that the collapse of the goaf after upper strata mining significantly affects the stress distribution in the coal pillar area. To ensure safety during mining, roadway excavation and working face recovery should be conducted after the upper strata have fully collapsed during strata mining. The co-mining working face roadway should be positioned beneath the original upper strata goaf, avoiding stress concentration areas in the coal pillar location. Ultimately, it is determined that the side roadway for the lower strata working face should be arranged with an offset of 10 m outward. Practical on-site experience has demonstrated that under this offset, there is minimal deformation of the surrounding rock in the coal pillar side roadway, meeting the safety production requirements of the working face.

A new non-pillar mining technology, gob-side entry retaining by roof cutting (GERRC), different from the conventional gob-side entry retaining formed by a roadside filling support, is introduced in this study. In the new technology, roof cutting is conducted so that the roof plate forms a short cantilever beam structure within a certain range above the retained entry, thus changing the stress boundary condition of the roof structure. To explore the deformation characteristics of the roof under this special condition, a short cantilever beam mechanical model was established and solved using energy theory and displacement variational methods. Meanwhile, a theoretical and analytical control solution for roof deformation was obtained and verified via field-measured results. Based on the aforementioned calculation, the relationship between the roof deformation and main influence parameters was explored. It was concluded that the rotation of the upper main roof and width of the retained entry had the most significant impacts on roof deformation. Bolt and cable support and temporary support in the entry had a non-obvious influence on the roof deformation and could not prevent the given deformation that was caused by the rotation of the upper main roof. Based on comprehensive theoretical analysis and calculation results, ideas and countermeasures to control short cantilever roof deformation—that is, designing a reasonable height of roof cutting and a controlled width of retaining entry—were proposed and tested. Field monitoring shows that the entry control effects were satisfactory.

With the increase of coal seam mining thickness, the caving height of stope roof, the mining-induced stress increase, and the control difficulty of gob-side entry retaining increase. To apply the gob-side entry retaining (GER) technology in thick coal seams, optimize the support method and reduce the deformation, based on directional energy-gathering blasting technology and roadside filling technology, gob-side entry retaining with synergistic roof cutting and roadside filling (GER-RCRF) is proposed. Through theoretical analysis, numerical simulation and field experiments, the mechanism and effect of the method are analyzed. The results show that due to the stress relief of roof cutting, the pressure of the solid coal rib and the roadside filling of the GER-RCRF is reduced, and the stress concentration area shifts to the deep rock mass. Under the condition of roof cutting, the stress of roadside filling is distributed in a “single peak”, and with the width increases, the peak stress first increases and then decreases, and then increases and then decreases. Meanwhile, the roof cutting height should be based on the broken and expansion effect of the rock strata, considering the key stratum effect of the rock layer. The stress of the surrounding rock is further reduced when the overlying key strata is cut off. Finally, the GER-RCRF has successfully reduced the stress of roadside filling, roof and solid coal rib, optimized the stress environment of surrounding rock, and successfully realized the purpose of gob-side entry retaining. The field test verified the effectiveness of GER-RCRF. The stress of roadside filling and the deformation of surrounding rock are significantly reduced. The research results provide a certain degree of scientific basis for the successful application of gob-side entry retaining in thick coal seam.HighlightsGob-side entry retaining with synergistic roof cutting and roadside filling (GER-RCRF) method is proposed based on directional energy-gathering blasting technology and roadside filling technology.Roof cutting can reduce the pressure of roadway surrounding rock, and roadside filling can support roof. The synergistic effect of the two can optimize the stress environment and reduce the deformation of surrounding rock.Comprehensive monitoring showed that GER-RCRF method effectively realizes the gob-side entry retaining in thick coal seam, meanwhile, reduces the deformation of surrounding rock and the stress of roadside filling.

To address the severe deformation and failure of roadway roof and floor encountered when crossing fault zones in coal mines in western China, this study takes the lower gateway of the 11E5-303 working face crossing the SF1 normal fault in Zhaohequan Coal Mine as an engineering case. A comprehensive investigation was conducted using field investigation, laboratory testing, numerical simulation, and engineering applications. The research aims to clarify the deformation mechanisms of the surrounding rock in fault-affected zones and to provide adequate control measures for roadway stability during fault crossing. Studies have shown that the roof and floor strata along the 11E5-303 Working face’s adjacent roadway are primarily composed of siltstone, fine sandstone, and argillaceous siltstone, which are highly susceptible to water-induced softening and swelling, leading to a significant decrease in mechanical strength. This phenomenon is particularly severe near the fault, where substantial roof subsidence and pronounced floor heave are observed. Based on the Mohr–Coulomb failure criterion, the deformation and failure mechanisms of the surrounding rock under the existing support system were analyzed. The study revealed that the roadway surrounding rock within 10 m of the fault zone is subject to intense deformation and damage, with the hanging wall showing a significantly larger failure range than the footwall. Floor heave at the fault zone is also markedly greater than in other sections. These findings identified key support zones and critical reinforcement areas, emphasizing the need for early implementation of high-strength support systems within the fault-affected area to enhance stability. Targeted control technology for surrounding rock stability in fault-crossing roadway was proposed. After optimization, the roof subsidence was reduced by 68% and the floor heaves by 81% compared to the original support system. The optimized support scheme significantly improved the stability of the roadway, demonstrating apparent effectiveness. These results provide valuable guidance for roadway support design and stability control under similar geological conditions.

Based on the elastic–plastic theory, the analytical formula of the second invariant J 2 of deviatoric stress at any point around the circular roadway under the non-uniform stress field is derived. The distribution law of J 2 of surrounding rock under the three-dimensional non-isobaric stress field is studied by theoretical analysis and numerical simulation. Combined with the butterfly failure theory of surrounding rock of roadway, the close relationship between the distribution pattern of J 2 and the distribution pattern of plastic zone is found, and the failure mechanism of surrounding rock is revealed. The results show that the distribution form of the second invariant J 2 of deviatoric stress is closely related to the distribution form of plastic zone. When the distribution of J 2 of surrounding rock shows ‘round’, ‘oval’ and ‘butterfly’, the plastic zone shows the corresponding consistent form. When the second invariant J 2 of deviatoric stress produces stress concentration, the surrounding rock of roadway will produce large-scale damage. When the stress concentration is high, it may lead to malignant expansion of surrounding rock of roadway. The distribution of the second invariant J 2 of deviatoric stress is directional. When the principal stress rotates over a certain angle, the second invariant J 2 of deviatoric stress rotates over the same angle as the plastic zone. Under the influence of superimposed mining, the second invariant deviatoric stress J 2 of the wind tunnel of Yangchangwan 160,206 working face presents butterfly distribution, and the stress butterfly leaves present a certain degree of rotation. Based on the failure mode of plastic zone, the corresponding optimization support scheme is proposed, and the engineering effect is good.

Large-diameter pressure relief boreholes are one of the primary measures for preventing coal mine rockburst. However, the implementation of these boreholes disrupts the original support structure of the roadway surrounding rock, leading to conflicts with surrounding rock control. Therefore, the pressure relief and energy dissipation behavior of variable-diameter boreholes in roadway surrounding rock was studied. Using a typical rockburst-prone coal mine as the engineering background. Based on elastic–plastic mechanics theory, the elastic solution for the stress distribution around the borehole and the extent of the pressure relief zone are analyzed. Numerical simulation software was used to study the effects of variable diameter drilling parameters (deep reaming diameter, deep reaming depth, and deep reaming spacing) on the pressure relief of roadway surrounding rock, energy dissipation in the roadway, and roadway deformation. The research results indicate that the distribution range of the pressure relief zone is influenced by the vertical stress, lateral pressure coefficient, cohesion, and internal friction angle of the coal body. The maximum radius of the pressure relief zone increases with the borehole diameter. As the deep reaming diameter increases and the borehole spacing decreases, the stress concentration in the surrounding rock of the roadway shifts more significantly toward the deeper region, making it easier to form a dual-peak stress zone. This enhances the pressure relief and stress transfer effect on the surrounding rock of the roadway, leading to greater energy dissipation. From the perspective of energy dissipation, it is concluded that the optimal location for the variable-diameter borehole should be within the peak vertical stress zone of the surrounding rock that has not been relieved. This study provides guidance for the prevention and control of dynamic disasters in deep coal and rock.

Aiming at the problem of surrounding rock control during the 52,102 working face passing through the roof fall area of return air roadway in lijiahao coal mine. Through on-site investigations, numerical simulations, and engineering practices, we analyzed the characteristics and causes of roof fall along the rib of the goaf. Based on the Mohr–Coulomb criterion, a numerical model was established, identifying influencing factors, and proposing an early intervention pressure relief control technology centered on \"proactive avoidance.\" Determined the starting position and the staggered distance of the avoiding roadway. The study indicates that: (1) The deformation of the surrounding rock in the roof fall roadway is mainly affected by high static loads, mining pressure, mechanical properties of the surrounding rock, and the effect of pressure relief. The optimal timing for implementing the best prevention technology is to stop mining and excavate an avoidance roadway when the working face is 20 m away from the roof fall area. At the same time, based on safety and economic principles, determine the distance between the avoiding roadway and the original roadway is 20 m to shorten the length of the working face. After passing through the avoidance roadway, resume the use of the original roadway to ensure economic benefits. (2) Early proactive intervention pressure relief technology effectively reduces the deformation of the roadway surrounding rock, decreasing the amount of deformation on both sides by about 11%, verifying its effectiveness and practicality.

To address the challenges of surrounding rock control in pre-driven roadways during the final mining stage of extra-thick coal seams, this study focuses on the 13,104 working face at Ciyaogou Coal Mine as a research background. Combining theoretical analysis, numerical simulation, and field engineering validation, the investigation examines stress distribution patterns, plastic zone evolution characteristics, and optimized support technology for surrounding rock under different lateral pressure coefficients (λ ≤ 1.0). Research findings reveal that: under varying lateral pressure conditions, circular roadway plastic zones predominantly develop three morphological types circular, elliptical, and butterfly-shaped. Roadway shoulder zones serve as the core areas for damage concentration, with failure progressively extending toward both sides. As the working face mining, peak stress primarily concentrates in the solid coal side’s secondary influence zone of the main pre-driven roadway, with plastic failure severity escalating from 20 to 96%. Plastic zones in the roadway roof and floor transition from the residual pillar side toward the protective pillar side. Side deformation significantly exceeds roof-floor displacement, demonstrating distinct zonal asymmetric failure mechanisms. Consequently, a partitioned asymmetric support system incorporating “solid coal single-anchor cable + coal pillar anchor cable truss and channel steel anchor cable” is proposed. Field applications demonstrate effective control of main roadway roof-floor and sides convergence within 200 mm, with anchor cable stresses remaining below yield limits. This study provides an effective technical solution for surrounding rock stability control in pre-driven roadways during the critical final mining stage.