Study on evolution law of internal deformation of soil mass corresponding to subsidence stretching area of thick loose layer mining areas：a case of Suntuan Coal Mine in Huaibei

To study the internal deformation evolution law of soil mass corresponding to subsidence stretching area of mining areas with thick loose layer, the No.10111-working face of Suntuan coal mine in Huaibei is selected, and No.1—3 vertical boreholes are arranged at 60 m spacing along the direction perpendicular to the advancing direction from the near to the distant for the loose layer corresponding to stretching area of the working face. In the process of coal mining subsidence, the borehole deformation monitoring is carried out based on the technology of optical fiber (borehole No.1) and inclinometer (borehole No.2—3). The area occupied by the overlying rock strata and loose layers mobilized by coal mining is considered as a deformation zone, and the concept of the movement angle of strata of arbitrary thickness is introduced. The results show that: The maximum depth at which strain occurs in the borehole No.1 is about 157 meters, with the deeper sections of the borehole reaching the active phase before the shallower; Within the monitoring range of boreholes No.2 and No.3, the geological formations can be divided from bottom to top into stable sections, lower, middle, and upper sections of the deformation zone. The final cumulative horizontal displacement at the borehole openings of No.2 and No.3 is 129.8 mm and 99.4 mm respectively, and the maximum displacement depths of about 108 m and 75 m respectively; Moreover, the horizontal displacement distribution of No.2 and No.3 borehole from bottom to top is generally uniform, and the average horizontal displacement per meter borehole is about 1.2 mm and 1.3 mm, respectively; In each borehole, the lower part of the deformation zone reaches the active period before the upper part and the upper part still has weak deformation after the lower part of the deformation zone is stable; For a certain thickness of strata in the loose layer, the movement angle increases with the increase of its depth, and the depth h of the lower boundary of the loose layer deformation zone decreases with the increase of the horizontal distance l from the working face, which accords with the exponential function relationship.