Roof weighting behavior and roof structure of large mining height longwall face in shallow coal seam

Based on a large amount of field observation in the Yushenfu mining area, the roof pressure at large mining height fully mechanized coal face in the shallow coal seam is obtained.The resistance of the large mining height face increases with the increase of mining height, and rapidly increases when the mining height is above 6 m.The dynamic load factor is 1.4 and has little change with mining height.The roof weighting steps are not changed with the mining height, and the first weighting step is 35-70 m, and the periodic weighting step is 9-20 m.The roof caving height is 2-4 times of the mining height.The peak abutment pressure decreases with the increase of mining height, and the peak position is about 2 times of mining height.According to the field observation and physical simulation, it is found that the large mining height causes high caving zone and “thick equivalent immediate roof” which leads to the hinge layer position of main roof structure move upward.According to the gob filling condition by caved immediate roof, the filling condition can be divided into sufficient filling type and general filling type.Based on the general filling condition which is more dangerous, the roof structural model of “high oblique step voussior beam” is proposed, and the calculation formula of the support rated resistance is put forward.Finally, the theoretical calculation formula of support rated resistance is verified.