Effect of working face length on underground pressure characteristics by fully-mechanized top-coal caving mining under shallow-buried thick bedrock loose roof

Based on the results of in-situ measurement and numerical simulation, the effect of working face length on underground pressure characteristics by fully-mechanized top-coal caving mining under the shallow-buried thick bedrock loose roof is studied. Some conclusions can be drawn as follows: (1) The increase of working face length has markable influence on the underground pressure characteristics; (2) the weighting span becomes shorter, the pressure on the support in the face is uniform, the pressure distribution is in the shape of an arch which regards the middle point of the working face as the symmetrical axis, and the regression relation between the maximum resistances and the initial ones is linear in the super-length fully-mechanized top-coal face; (3) there is a complex pressure arch varying with the length of the face; (4) with the increase of mining face length, the peak abutment pressure ahead of the working face increases, the height and rate of the flat along the face all increase, and the underground pressure behaviors are enhanced, which might be propitious for the top coal fracture; (5) the subsidence quantity of the top coal in the control area increases along with the face length in logarithmic way, but decreases along with the initial supporting force in negative logarithmic rule; (6) after assigning the subsidence, the regression relation between the initial supporting force and the face length is linear. The study results can be useful for choosing the reasonable face length and the support.