# Strata Movement of the Thick Loose Layer under Strip-Filling Mining Method: A Case Study
## 3 Numerical Simulation Analysis of Overburden Movement and Failure
### Influence of Filling Ratio on Movement and Failure of Overburden  
(1) Analysis of overburden and surface deformation  
After four rounds of strip filling mining with different filling rates, the movement and deformation of overburden and surface are shown in Figure 4.  
As can be seen from Figure 4, in strip paste filling mining, the filling rate decreases and the surface subsidence value increases significantly. The surface subsidence value is the largest in the mining center of the working face, and the subsidence value is symmetrical. When the filling rate is 98%, 97%, and 95%, the maximum surface subsidence values are 180 mm, 287 mm, and 377 mm, respectively. When the filling rate is 98%, 97%, and 95%, the surface horizontal displacement ranges are 92 mm\(--\)86 mm, 148 mm\(--\)135, mm and 200 mm\(--\)173 mm, respectively. The increase of surface subsidence and horizontal displacement makes the horizontal deformation and increases the inclined deformation \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Rock Formation**} & \multirow{2}{*}{\begin{tabular}{c} **Thickness** \\ **/m** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Density** \\ **/kg/m3** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Bulk** \\ **Modulus** \\ **/MPa** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Shear** \\ **Modulus** \\ **/MPa** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Tensile** \\ **Strength** \\ **/MPa** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Internal Friction** \\ **Angle** \\ **/MPa** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Cohesion** \\ **/MPa** \\ \end{tabular} } \\ \hline Aeolian sand & 5.5 & 1650 & 133 & 79 & 0.00 & 8 & 0.00 \\ Lishi loess & 88.2 & 1950 & 233 & 185 & 0.20 & 10 & 0.01 \\ Silty clay & 75 & 2240 & 609 & 469 & 1.20 & 25 & 0.02 \\ Medium coarse sandstone & 22.4 & 2250 & 1436 & 1062 & 2.50 & 40 & 2.81 \\ Sandy mudstone & 2.6 & 2430 & 1047 & 1028 & 0.85 & 41 & 1.93 \\ Coal seam & 10.4 & 1420 & 340 & 300 & 0.50 & 36 & 3.40 \\ Argillaceous siltstone & 30 & 2760 & 780 & 402 & 3.90 & 39 & 3.14 \\ Filling body & — & 1990 & 389 & 233 & 1.00 & 24 & 0.79 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mechanical parameters of surrounding rocks. Figure 3: Numerical calculation model diagram. and curvature. The law of roof subsidence is consistent with that of surface subsidence. When the filling rate is 98%, 97%, and 95%, the maximum subsidence values of the roof are 203 mm, 319 mm, and 395 mm, respectively. Among them, the stripped roof subsidence values of different rounds of mining and filling are also different. The strip roof subsidence of the fourth round is the largest, followed by the third round and the second round, and the first round is the smallest. This also shows that the roof subsidence value gradually accumulates with strip mining. (2) Stress analysis of overburden and backfill  
After four rounds of strip filling mining with different filling rates, the vertical stress change curve of the filling body and the tensile stress curve of the roof is shown in Figures 5-7, respectively. As can be seen from Figure 5, the coal walls on both sides will produce certain stress concentrations after strip paste filling mining, and the magnitude of stress concentration will change with the change in filling rate. When the filling rate is 98%, 97%, and 95%, the  
Figure 4: Curves of overburden and surface deformation with different filling rates. (**a**) The ground sinks, (**b**) Horizontal displacement of the ground surface, (**c**) The roof sinks. peak values of advance bearing stress are 8.96 MPa, 9.63 MPa, and 9.25 MPa, respectively. The stress concentration factors are 2.67, 2.86, and 2.75. As can be seen from Figure 6, after the four strips mining face with paste filling is fully mined, the stress of filling body in different circulating strips is different.