Abstract
Due to the large number of layers and different thickness of partings, the poor caving performance of top coal (CPTC) in thick coal seam with complex structure has always been an important problem affecting the top-coal recovery rate (TCRR) in the fully mechanized caving face. Based on the theory of coal-caving ellipsoid, a mechanical model of a long cantilever structure formed by the fracture of the thick parting crossing coal-caving ellipsoid was established, and the influence mechanism of the long cantilever beam structure on CPTC was revealed. Besides, a method to distinguish the influence of multi-layer partings on CPTC was put forward, and the influence of parting thickness, position and the number of parting layers on CPTC was obtained. The results show that the critical parting thickness hg increases with the increase of axial deflection angle θ, mining thickness h and volume weight of parting γg, and hg decreases with the increase of tensile strength of the parting Rt. The main influencing factors of hg can be ordered as follows: h > θ > Rt > γg. The position of the thick parting plays a controlling role in CPTC. The fundamental measure to improve CPTC is to reduce the cantilever beam length formed by the thick parting so that top coal above the parting can be caved. Based on this, the technical scheme of hydraulic fracturing for promoting top-coal caving was proposed and applied. During the initial mining period of the working face, TCRR was effectively increased from 45.99 to 77.18%.
Highlights
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The influencing factors of the critical thickness of partings affecting the caving performance of top coal include h, θ, Rt, and γg.
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The layer of thick parting plays a controlling role in the caving performance of top coal of coal seam with multi-layer partings.
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A scheme of hydraulic fracturing to reduce the cantilever beam structure formed by the fracture of partings was proposed and applied.
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Data Availability
The data are available from the corresponding author on reasonable request.
Abbreviations
- CPTC:
-
Caving performance of top coal
- TCRR:
-
Top-coal recovery rate
- h g :
-
The critical parting thickness of affect CPTC
- θ :
-
Axial deflection angle of coal-caving ellipsoid
- h :
-
Mining thickness
- γ g , γ m :
-
Volume weight of parting and coal
- R t :
-
Tensile strength of the parting
- L :
-
The critical length of the parting across the coal-caving ellipsoid
- M max :
-
The maximum bending moment of the cantilever beam structure
- q m :
-
The uniform load transmitted from the upper coal seam to the parting
- q g :
-
The dead weight of parting
- J :
-
Section modulus
- σ max :
-
Maximum tensile stress
- h m :
-
The thickness of the top coal above the parting
- a, b, c :
-
Half of the major axis and two minor axes of the ellipsoid
- ε :
-
The eccentricity of the caving body
- h' :
-
The height from the parting to the coal seam floor
- α :
-
The caving angle of coal
- f :
-
The Proctor hardness coefficient
- h i :
-
The thickness of parting i
- ∆h i :
-
The thickness of the coal between parting i and parting i + 1
- l i :
-
The critical cantilever beam length of parting i that have an impact on CPTC
- q i :
-
The loading of top coal between parting i and parting i + 1
- H r :
-
The thickness of roof r above the coal seam
- γ r :
-
The volume weight of roof r above the coal seam
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Acknowledgements
This work was supported by the National Key Research and Development Program of China (No. 2018YFC0604705), and the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi (No. 2021L580).
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ZC: methodology, software, formal analysis, investigation, writing—original draft. XW and DQ: resources, writing—review and editing, supervision, data curation. YZ, XC and ZN: investigation, writing: review and editing. JW: writing: review and editing.
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Chang, Z., Wang, X., Qin, D. et al. Study on a Mechanical Model of a Long Cantilever Beam Structure Formed by the Fracture of Thick Partings Transversely Penetrating a Coal-Caving Ellipsoid and Its Application. Rock Mech Rock Eng 57, 1153–1169 (2024). https://doi.org/10.1007/s00603-023-03611-w
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DOI: https://doi.org/10.1007/s00603-023-03611-w