The Mechanical Model on Surface Subsidence Caused by Backfilling Mined-Out Area on Thick Loose Loess Layer: Taking a Sedimentary Bauxite Mine as an Example

To study the influencing factors of surface subsidence by the backfilling of a mined-out area on thick and loose loess layers, a mechanical model on synergic deformation and surface subsidence is constructed taking the case of a sedimentary bauxite mine in China’s Shanxi province as an example. Backfill state is classified based on the position of the protective roof and the backfill body. The influence of different filling ratios, the thickness of overlying loess, and the stope span on surface subsidence are quantitatively analyzed. The results reveal that: (1) When the thickness of the overlying loess Hg and the stope span s are constant, surface subsidence ωmax is negatively correlated with the filling ratio η. When η reaches the state III inflection point, the amplitude of surface subsidence ωmax declines sharply and eventually tends to be stable. (2) When the filling ratio η and stope span s are constant, surface subsidence ωmax is negatively correlated with the thickness of the overlying loess Hg, and the growth ratio decreases continuously. (3) When η and Hg are constant, surface subsidence ωmax is positively correlated with s, and the growth ratio increases continuously. In the end, the validity of the theoretical calculation is verified by numerical simulation and an engineering case example.