Effect of floor failure in fully mechanized caving of extra-thick coal seam in Datong Mining Area

To study the floor deformation and failure characteristics in fully mechanized caving of extra-thick coal seam of 8209 working face in Tongxin Coal Mine was selected as the background, and the strain induction method was used to perform the field measurement. According to the variation trend of different strain sensors of coal seam floor, the deformation and failure depth of coal seam floor was determined to be between 19.8 m and 21.9 m. The distribution characteristics of mining ground pressure in the horizontal direction of floor were explored, and it was found that the periodic weighting step distance of floor was far less than that of roof. At the same time, based on the engineering geological model and similarity theory of 8209 working face, a physical model test of similar materials in mining floor was tested. Through the macroscopic model of mining floor crack expansion and the change in stress increment of four monitoring sections, it was found that the closer the coal seam, the greater the vertical stress increment, and the smaller the change towards the deep. The vertical stress increment of floor rock mass 22 m away from the coal seam is no longer affected. Therefore, it was inferred that the failure depth of mining floor in this working face is no more than 22 m, consistent with the field measurement results. The results show that the extra-thick coal seam in fully mechanized caving has an important cushioning effect on the propagation of floor mining pressure.