Key Takeaways & Executive Findings
- •• A novel control method combining roof cutting and confined concrete columns effectively stabilizes roadways in extremely close-distance coal seams. • The proposed roof structure model of 'voussoir beam of upper layer + short cantilever beam of lower layer' provides a theoretical basis for stability analysis. • Field tests demonstrate significant reduction in support stress and high-strength support in dynamic influence zones, meeting safety deformation requirements. • The method offers effective guidance for practical application in extremely close-distance coal seams, addressing large deformation failures.
Abstract
Under the influence of the upper coal pillars and dynamic pressure of coal mining, the roadway of the lower coal seam is prone to large deformation failure. In this paper, a novel control method and key technologies of automatically formed roadway (AFR) by roof cutting and confined concrete column in extremely close-distance coal seam are proposed. Furthermore, a numerical model is established to analyze the structure characteristics of overlying roof strata. Based on numerical results, the roof structure model of “voussoir beam of upper layer + short cantilever beam of lower layer” of this method is proposed. What’s more, the calculation equation of the roof bending moment and evaluation indexes is established, and the influence of different factors on roof stability control of AFR is studied. Finally, a field test is conducted to verify the effectiveness of this novel method. Field results were as follows: 1) The maximum and average support stress of working face obviously decreased; 2) The confined concrete column can provide high-strength support in dynamic influence zone; 3) The maximum deformation of AFR safety requirement can be met. This study can provide effective guidance for the application of this method in extremely close-distance coal seam.
1. Introduction
Under the condition of extremely close-distance coal seams, a large deformation of surrounding rock easily occurs in the roadway of the lower coal seam and support materials break off [1−3]. Especially in the extremely close-distance coal seam, the interlayer spacing is generally 5 −10 m, and the safety control of roadway surrounding rock is particularly difficult [4−6].
At present, many experts have made lots of contributions to extremely close-distance coal seam, including overlying strata movement law, reasonable roadway and coal pillar layout, pressure relief measures and high-strength support of roadway [7 −10]. In terms of overlying strata movement law, GHABRAIE et al [11, 12] used the physical simulation method to study the characteristics of multi-seam mining subsidence and proposed a subsidence prediction method. ADHIKARY et al [13] conducted the numerical simulation of surface subsidence. In terms of reasonable roadway layout and coal pillar layout, GHOSH et al [14] provided reasonable chain pillar design at the deepest multi-seam longwall workings in India. CHEN et al [15] analyzed the influence of different stopping positions through numerical simulation, and further verified it through model tests. In terms of pressure relief and high-strength support of roadway, YIN et al [16] proposed a new technology of borehole pressure relief according to the characteristics of high-stress concentration under the remaining coal pillar, and verified its feasibility by field tests. SHANG et al [17] expounded the deformation characteristics of roadway in close coal seams and put forward the reasonable control technology. CAO et al [18] proposed the overall scheme of roadway roof using ultra-high strength yielding bolt + steel mesh + M-shaped steel belt + anchor cable. In terms of support technology of confined concrete column, WANG et al [19] comprehensively summarized and analyzed the research progress of confined concrete support theory and technology for underground engineering. WEI et al [20] investigated the compressive behavior of circular steel tube-confined reinforced ultrahigh performance concrete columns and established a reasonable formula for predicting the bearing capacity. However, the current technologies of close-distance coal seam cannot change the mining pressure influence caused by remaining coal pillars and cannot effectively cut off the long cantilever beam, resulting in the difficulty of controlling the large deformation of roadway roof structure.
In fact, the method of automatically formed roadway (AFR) by roof cutting can effectively reduce the roadway stress and eliminate the remaining coal pillars [21 −23]. At present, this method has been applied under different geological conditions.
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XUE Hao-jie, WANG Qi, ZHANG Chong, HE Man-chao, ZHANG Bo-wen, ZHANG Shu, WANG Ye-tai (2025). A novel control method of automatically formed roadway by roof cutting and confined concrete column in extremely close-distance coal seam. Journal of Central South University. https://doi.org/10.1007/s11771-025-6080-6
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Frequently Asked Questions
What is the novel control method proposed in this paper?
The novel control method combines roof cutting and confined concrete columns to stabilize roadways in extremely close-distance coal seams, addressing large deformation failures.
How does the roof structure model contribute to the study?
The proposed roof structure model of 'voussoir beam of upper layer + short cantilever beam of lower layer' provides a theoretical basis for analyzing roof stability and optimizing support design.
What were the key findings from the field test?
Field results showed decreased support stress, high-strength support in dynamic influence zones, and deformation within safety requirements, validating the method's effectiveness.
What is the significance of this research for coal mining?
This research offers an effective approach to control roadway stability in extremely close-distance coal seams, improving safety and efficiency in mining operations.
What methods were used in this study?
The study employed numerical simulation to analyze roof structure, theoretical modeling for roof bending moment, and field tests to verify the proposed method.
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