## 3 Results
### Early-Warning Indicator System  
Instrument monitoring is a necessary part of underground construction. Different monitoring items have different impacts on pit safety. Analyzing all the monitoring data is not necessary and makes the calculation too complicated. Therefore, in accordance with the principle of indicator selection, the number of indicators is reasonably reduced on the premise of ensuring accuracy and comprehensiveness. The distribution of monitoring \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Stratum** & **Category** & **Code** & **Name of Rock** & **Water Content (\%)** & **Natural Density (g/cm\({}^{3}\))** & **Void Ratio** & **Stratigraphic Characteristics** \\ \hline Q\({}_{\text{a}}\)\({}^{\text{m}}\) & \begin{tabular}{c} Reclamation \\ soil layer \\ \end{tabular} & \textless{}1-1\textgreater{} & \begin{tabular}{c} Miscellaneous \\ Fill \\ \end{tabular} & 43.3 & 1.49 & 1.650 & \begin{tabular}{c} It is composed of fly ash, clay, sand, and concrete \\ blocks, and the soil \\ is uneven. \\ Gray black, flow plastic, \\ high compressive soil, \\ mainly clay, containing a \\ small amount of sand. \\ Gray, saturated, loose, \\ slightly dense, mainly \\ quartz sand, local silt. \\ \end{tabular} & \begin{tabular}{c} It is composed of fly ash, clay, sand, and concrete \\ blocks, and the soil \\ is uneven. \\ Gray black, flow plastic, \\ high compressive soil, \\ mainly clay, containing a \\ small amount of sand. \\ Gray, saturated, loose, \\ slightly dense, mainly \\ quartz sand, local silt. \\ \end{tabular} \\ Q\({}_{\text{a}}\)\({}_{+}\)\({}^{alp}\) & \begin{tabular}{c} Continental \\ alluvial- \\ poluvial layer \\ \end{tabular} & \textless{}4N-2\textgreater{} & \
\begin{tabular}{c} Cohesive Soil \\ Layer \\ \end{tabular} & 27.9 & 1.96 & 0.771 &
\begin{tabular}{c} It is grownly below, hard \\ plastic to hard, mainly \\ powder and clay, \\ containing powder fine \\ sand and medium sand. \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Foundation pit geotechnical parameters. Figure 2: (**a**) Station plan. (**b**) Section view of station. points is shown in Figure 3, with a total of 20 monitoring points. Given comparable deformation patterns and shared deployment principles across monitoring points, six representative locations (C1, C5, C11, C14, C15, C18) were selected for analysis. Items and related configuration are shown in Table 2.  
Combined with references [38; 39] and the risk characteristics of this project, the surface settlement, groundwater level, and pile horizontal displacement are selected as the risk early-warning indicators. In the actual construction process, the control value is an important basis for judging the safety status of the project structure and the surrounding environment. According to the relevant specifications and the data provided by the relevant supervisory company, the control value of this metro pit project is controlled by the cumulative value and the rate of change, as shown in Table 3.  
Considering that the early-warning results and the actual monitoring values have trend uniformity, this paper takes the control value as the benchmark value and takes the ratio \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Monitoring Items** & **Location and Monitoring Objects** & **Measuring Point Position** & **Numbers** & **Monitoring Equipment** \\ \hline \multirow{4}{*}{surface subsidence} & Soil around the foundation & The horizontal spacing of monitoring points is about 20–30 m, and there are two monitoring points in the monitoring section. & \multirow{4}{*}{91} & Level instrument, \\  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Monitoring items and related configuration. Figure 3: Layout of monitoring points for the Luochongwei station project. Cx represents the location of the monitoring point, x = 1, 2, 3,.., 20.