## 3 Results
### Results of the Land Damage Assessment  
When choosing indicators for assessing land damage, it is important to thoroughly evaluate the specific conditions of the subsidence area. Indicators that accurately reflect the extent of land damage in the subsidence area should be selected, taking into account the results of on-site assessments. The primary types of collapses in the research area are collapse basins and collapse waterlogging. The waterlogged areas within the collapse zones should be effectively exploited to enhance water utilization efficiency. When assessing the extent of land damage in the non-waterlogged areas within the collapse zone, the first factor to consider should be the index of collapse depth. The land damage evaluation indexes in the Zhaogu Mining Area, as indicated in Table 6, were selected based on the study findings of [PERSON] (2018) and [PERSON] (2018). The land damage evaluation results in the subsidence area were utilized to create a vectorized thematic map using ArcGIS (v.10.6.1), as shown in Figure 11. The land damage in the subsidence area was categorized into three levels: minor damage, moderate damage, \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Evaluation Index**} & \multirow{2}{*}{**Acquisition Method**} & \multicolumn{3}{c}{**Grading Standard**} \\ \cline{3-5}  & & **Minor Damage** & **Moderate Damage** & **Severe Damage** \\ \hline \multirow{2}{*}{Subsidence value (cm)} & D-InSAR result & \textless{}100 & 100–200 & \textgreater{}200 \\  & Statistical yearbook & \textless{}20.0 & 20.0–60.0 & \textgreater{}60.0 \\  & Slope (cm/m) & DEM data & \textless{}10 & 10–15 & \textgreater{}15 \\ Soil layer thickness (m) & Field investigation & \textgreater{}1.5 & 0.8–1.5 & \textless{}0.8 \\ Organic matter (\%) & Field sampling determination & \textgreater{}1.5 & 0.5–1.5 & \textless{}0.5 \\ PH value & Field sampling and detection & 6–8 & 5–6 or 8–8.5 & \textless{}5 or \textgreater{}8.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Selection and classification standards for land damage indicators in subsidence areas. Figure 10: Change of the proportion of land use type in Zhaogu No. 1 Mine and No.2 Mine subsidence area from 2017 to 2021.  
and severe damage. The size of every level of damage was quantified and recorded in Table 7. Minor damage refers to a situation where the land has suffered just slight damage that does not significantly impact its normal functioning. Moderate damage refers to a situation where the damage inflicted on the land is more severe and has a significant impact on its overall functionality. Severe damage refers to the significant destruction of land, resulting in the loss of its original functionality. Table 7 reveals that the waterlogged region within the subsidence zone measures 783.36 \(\mathrm{hm}^{2}\), or 41.65% of the total area of the subsidence zone. The extent of land destruction within the collapse zone is mostly characterized by minor and moderate levels, which collectively make up 55.16% of the entire area of the collapse zone. The minor damage region covers 437.67 \(\mathrm{hm}^{2}\), which is 23.27% of the subsidence zone. The moderate damage area is 599.85 \(\mathrm{hm}^{2}\), accounting for 31.89% of the subsidence zone. The severe damage area covers 60.11 \(\mathrm{hm}^{2}\), representing 3.19% of the subsidence zone. The damage degree of different types of land in subsidence zones is determined by combining the land use information in those areas. Table 8 displays the findings of the classification of damage degree for different types of land in places affected by subsidence. The extent of damage to agricultural land, construction land, and idle land is primarily categorized as mild or moderate, with relatively fewer instances of severe damage.