Downhole testings and numerical simulations on flaking of iron sulfide concretions in different coal wall depths with different drum pick points were carried out in the study, and the flaking mechanism was analysed. The research showed that through failure damage area with intensive cracks in the coal around the concretion was shaped under the loading of pick. There were four flaking types: translational flaking, rotating flaking, indentation flaking and truncation flaking. The flaking force of concretions in different coal wall depths with different drum pick points were different. The flaking force decreased with the deepening of the concretion's position. The flaking force was smaller with pick point near the end than in the center of concretion.


In China, the thin coal seam is abundant and widely distributed. The explored thin seam reserves is 6.1 billion tons, about 20.4% of total recoverable reserves[1]. As the important coal production base, China takes a pole position in thick seam fully mechanized coal caving. But because of lack in thin seam fully mechanized technical equipments with good adaptability and high efficience, the thin seam coal caving is one relative weakness[2,3].

The thin seam reserves in Yanzhou Mining Area is 1.496 billion tons, and the recoverable is 0.133 billion tons, about 22.1% of the total recoverable reserves. There are high hardness (f=8&126;12) and different sizes iron sulfide concretions randomly distributed in the seam, which bring great difficulties to mechanical mining[4–8]. The key in realizing mechanical mining in thin seam is the concretions' flaking. In the paper the flaking mechanism of concretions in thin seam were analysed, which provided theoretical basis for equipment development and caving technology.

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