1507 low recovery rate, high gangue content, complex production organization, and increased safety risks, particularly in hard and thick roof conditions. These shortcomings have increasingly constrained the development of high-capacity modern mines. To overcome these limitations, China initiated a major engineering effort to explore the feasibility of fully mechanized longwall mining with a single-pass cutting height of 10 m. Centered on the Caojiatan Coal Mine, this project targeted the world’s first application of 10-m fully mechanized longwall mining in an extra-thick coal seam. The core objective was to break the long-standing mining-height limit by addressing surrounding-rock control, key equipment reliability, and system-level coordination under extreme conditions. In this paper, we present a concise overview of the geological challenges, key enabling technologies, system integration, and field performance of the world’s first 10-m fully mechanized longwall mining operation. The successful implementation of this project establishes a new upper limit for longwall mining height and represents a significant breakthrough for extra-thick coal seam development. 2. GEOLOGICAL CONDITIONS AND ENGINEERING CHALLENGES 2.1 Geological Conditions of the 10-m Longwall Face The world’s first 10-m fully mechanized longwall mining operation was implemented at the working face 122104 of the Caojiatan Coal Mine, located in the Yushen mining district, Shaanxi Province, western China. The mine exploits the 2-2 coal seam, which is characterized by stable occurrence, simple geological structure, and favorable regional mining conditions. The coal seam thickness along the working face ranges from approximately 7.2 m to 12.3 m, with an average thickness of about 10.5 m, making it representative of extra-thick coal seams that are traditionally difficult to mine using single-pass methods. The seam dip is gentle, generally less than 6°, and the coal strength coefficient ranges from 2 to 3, indicating a hard coal seam. The burial depth of the working face varies from approximately 270 m to 360 m, corresponding to moderate in-situ stress levels. 2.2 Thick and Hard Roof Structure A defining geological feature of the Caojiatan Coal Mine working face is the presence of multiple layers of thick and hard sandstone roof strata above the coal seam. Within approximately 100 m above the seam, several sandstone layers with individual thicknesses of 10–30 m are developed, exhibiting high strength and good integrity. In-situ testing indicates uniaxial compressive strengths commonly exceeding 60 MPa, with some layers approaching 100 MPa. These thick and hard roof strata do not readily cave after coal extraction, resulting in large suspended roof areas and strong periodic weighting behavior. Field investigations reveal a typical multi-layer “thick hard roof assemblage”, forming a complex overburden structure that significantly amplifies mininginduced stresses during large-height extraction. A simplified stratigraphic profile of the roof structure is recommended as Fig.1, highlighting the vertical distribution and thickness of key hard roof layers (green in Fig. 1) that control strata behavior.
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