由于煤层沉积环境的变化,顶板岩性决不是单一的,特別是煤层群,经常含有数量不同的薄煤或炭质页岩。加淮南煤田,煤层顶板岩性变化很大,在14～15层可采煤层间夹有0.2～0.6m成组或单一赋存的薄煤(或炭质页岩)20～22层。他们距可采煤层的距离远近不一,自3.0～5.0m 到不足1.0m。均在放顶后的冒落范围内。我们将直接顶中含有薄煤或炭质页岩的煤层顶板称为复合直接 Due to changes in the sedimentary environment of the coal seam, roof lithology is by no means single, especially coal seams, often containing thin coal or carbonaceous shales in varying numbers. In Huainan coalfield, the lithology of the roof of the coal seam varies greatly. There are 20 ~ 22 layers of thin coal (or carbonaceous shale) of 0.2 ~ 0.6m group or single occurrence in the 14 ~ 15th coal seam. They are close to the coal seam distance, from 3.0 ~ 5.0m to less than 1.0m. Are in the caving area within the roof. We refer to the roof of a coal seam directly containing thin coal or carbonaceous shale as a composite direct