Key Takeaways & Executive Findings
- •• Undulation height and period significantly affect coal wall mechanical parameters, with height having a more pronounced effect; undulating surfaces reduce strength to 50-60% of flat surfaces. • Failure under uniaxial compression is predominantly tensile, producing long slender fragments with a characteristic 'III'-shaped fracture pattern. • Energy dissipation occurs at all loading stages for undulating surfaces, with a higher proportion in the early stage due to structural damage and internal crack formation. • Reducing the elastic modulus of the support plate material alleviates stress concentration at convex locations and increases peak strength.
Abstract
Coal wall stability is a critical factor influencing coal mining efficiency and threatens the safety of working faces, where irregular coal wall surfaces significantly affect the contact and support effectiveness of the support plate, thereby impacting stability. Through a combination of theoretical analysis, mechanical testing, and numerical simulations, this study establishes a mechanical model of irregular coal wall surfaces to investigate the effects of the undulation period and undulation height on coal wall failure characteristics. This research reveals the mechanical response mechanisms of irregular coal wall surfaces and proposes an innovative method to enhance coal wall stability by improving the supporting cushion material of the support plate, which was validated through numerical simulations. The results show that the undulation height and undulation period significantly influence the macroscopic mechanical parameters of the samples, with the undulation height exerting a more pronounced effect. The strength of the samples with undulating surfaces is approximately 50%–60% that of the samples with flat surfaces. The failure mode under uniaxial compression is predominantly tensile, resulting in long and slender block fragments with a characteristic ''III''-shaped tensile fracture pattern. During the loading process, samples with undulating surfaces dissipate energy at all stages, with a greater proportion of energy dissipation occurring during the early loading stage because of structural damage and the formation of internal cracks. The surface compressive and tensile stresses are correlated with the curvature radius of the convex surface and the elastic modulus of the supporting plate. Reducing the elastic modulus of the supporting plate material can effectively alleviate the stress concentration at convex locations and increase the peak strength. This study provides theoretical foundations and technical references for the prevention and control of coal wall spalling in deep thick coal seam mining.
1. Introduction
In high-intensity mining operations, the instability of coal walls has become a major hazard, significantly limiting the safety and efficiency of modern comprehensive working faces. Most existing studies on coal wall spalling have assumed flat coal walls, where full contact is made between the coal wall and the supporting mechanisms [1–3]. However, under practical mining conditions, coal walls often exhibit irregular, undulating profiles [4], leading to line or even point contact between the support plate and the coal wall, as illustrated in Fig. 1. Therefore, understanding the impact of surface irregularities on coal wall failure characteristics and proposing targeted support strategies are crucial for ensuring coal wall stability.
Several researchers have conducted extensive experimental investigations into the morphology and mechanical responses of coal-rock masses with uneven surfaces or structural planes. Wang [5] studied the distribution characteristics of structural planes within coal bodies via a comprehensive approach and developed a synthetic coal body model. The study analyzed the strength, deformation, and fracture development of the coal body under various conditions.
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Jiachen Wang, Xiang Yu, Zhong Huang, Lianghui Li, Yubing Wang (2025). Impact of surface irregularities on coal wall stability and support mechanisms: Insights from physical and numerical experiments. SinoTechIntel Verified Research. https://doi.org/10.1016/j.ijmst.2025.06.011
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Frequently Asked Questions
What is the main focus of this study?
The study investigates the impact of surface irregularities (undulation height and period) on coal wall stability and support mechanisms, using physical and numerical experiments to propose improved support strategies.
How do surface irregularities affect coal wall strength?
Samples with undulating surfaces have approximately 50-60% of the strength of flat-surfaced samples, with undulation height having a more pronounced effect than period.
What failure mode is observed in coal samples with undulating surfaces?
The failure mode under uniaxial compression is predominantly tensile, resulting in long slender block fragments with a characteristic 'III'-shaped tensile fracture pattern.
What innovative method is proposed to enhance coal wall stability?
The study proposes improving the supporting cushion material of the support plate, specifically reducing its elastic modulus, to alleviate stress concentration at convex locations and increase peak strength.
What are the practical implications of this research?
The findings provide theoretical foundations and technical references for preventing and controlling coal wall spalling in deep thick coal seam mining, improving safety and efficiency.
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