(1) Fallen belt. After the break, the rock blocks are irregularly degraded, and the arrangement is also extremely irregular. The looseness coefficient is relatively large, generally up to 1.3 to 1.5. However, after re-compacting, the coefficient of expansion can be reduced to about 1.03. This region of coal mined adjoining layer, in many cases due to the backward run by roof formed.
(2) Crack zone. After the rock stratum is broken, the area where the rock blocks are still arranged neatly is the crack zone. It is located above the falling belt and has a small coefficient of expansion due to the neat arrangement. It is possible for the critical layer to break the block to form the "masonry beam" structure shown in Figure 2-137(c). The fall zone and the crack zone are collectively referred to as the "two zones", also known as the "water-conducting fracture zone", which means that the overburden aquifer is located within the "two zones" and will cause the rock mass water to flow through the fracture of the rock mass. Goaf and coal mining face. The height of the “two belts†is related to the lithology and the mining height of the coal seam. The harder the lithology of the overburden, the greater the height of the “two beltsâ€. In general, for soft rock formations, the height of the “two belts†is 9 to 12 times that of mining height, 12 to 18 times for medium hard rock formations, and 18 to 28 times for hard rock formations. Accurately determine the height of the "two belts", and solve the damage caused by different types of overburden after actual mining measured in Figure 2-137. - Fallen belt; 2 - Crack zone (a) Overburden is soft The rock formation; (b) the overburden is a medium hard rock formation; (c) the overburden is a hard rock coal problem and the lower liberation layer is particularly important for mining gas outburst coal seams.
(3) Curved belt. All rock layers from the top of the fracture zone to the surface are called curved zones. The remarkable feature of the movement of the rock within the curved zone is the continuity and integrity of the movement of the rock formation, that is, the movement of the rock formation above the top of the fracture zone to the surface is layered and integrated. In the vertical section, the upper and lower sides are respectively The partial sinking difference is small. If there is a thick hard key layer, a separation zone may appear in the curved band.
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