## 2 Project Overview  
The launching section of the depot access tunnel on the Guangzhou Metro Line 10 in Guanggang New City is located in Liwan District, Guangzhou. The tunnel extends northwest from the launching shaft at the Guanggang New City depot. According to existing research [19; 20], when the cover-to-span ratio (i.e., the ratio of overburden depth to tunnel span) is less than 0.6, tunnel excavation has a significant impact on surface settlement and is thus defined as a shallow-buried tunnel. In this case, the average overburden depth of the launching section is 3.5 m, and the tunnel span is 6.4 m, giving a cover-to-span ratio of 0.55, classifying it as a shallow-buried tunnel. Based on analysis of geological investigation data and the characteristics of the shallow-buried muddy soil layer in the launching section, a slurry balance shield method is proposed for construction. The specific project location is illustrated in Figure 1.  
The stratigraphy at the tunnel face of the launching section, from top to bottom, consists of: <1> miscellaneous fill (1.7 m), <2-1A> muddy soil layer (1.5 m), <4N-2> silty clay (3.5 m), <5N-2> silty clay (5.19 m), <6> completely weathered coarse sandstone (4.6 m), <7-1> strongly weathered coarse sandstone (2.2 m), and <8-1> moderately weathered coarse sandstone (14.6 m). The tunnel face of the launching section is primarily located in silty clay strata. Field investigation determined that the groundwater level is approximately 3.5 m. In the project area, groundwater recharge is mainly from surface precipitation. The shield launching section is located in a silty clay layer and the upper muddy soil layer has been reinforced by replacement filling. Most of the nearby ground surface is covered with concrete pavement, so infiltration recharge from upper strata is negligible. Drainage is carried out via an internal drainage channel at the tunnel invert and grouting reinforcement was applied around the surrounding strata during construction. Therefore, groundwater influence on settlement can be ignored. According to the site investigation report, the physical and mechanical parameters of each soil layer are listed in Table 1.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \begin{tabular}{c} **Ground** \\ **Level** \\ \end{tabular} & **Soil Layer Name** & **Intensity/fg/cm\({}^{3}\)** & **Water** \\ \begin{tabular}{c} **Content/\%** \\ \end{tabular} & **Ratio/\%** & **Modulus** \\ \begin{tabular}{c} **Compress-** \\ **ibility/MPa** \\ \end{tabular} & **Modulus** \\ \begin{tabular}{c} **Ins/MPa** \\ \end{tabular} & **Coeffi-** \\ \begin{tabular}{c} **client/(m/d)** \\ \end{tabular} & **Cohesion/KPa** & **Efficient Angle/\({}^{\prime}\)** \\ \hline \textless{}1> & Miscellaneous fill & 2.02 & 32.2 & 62.2 & 4.38 & 10 & 0.1–2 & 15.0 & 12.0 \\ \textless{}2-1A> & Mucky soil & 1.54 & 73.8 & 199.4 & 1.89 & 2 & 0.001 & 6.0 & 4.0 \\ \textless{}4N-2> & Simely clay & 1.99 & 25.5 & 72.2 & 5.17 & 12 & 0.050 & 19.2 & 12.6 \\ \textless{}6> & \begin{tabular}{c} **constructed coarse** \\ \end{tabular} & 2.03 & 20.0 & 60.5 & 5.47 & 60 & 0.400 & 26.0 & 20.0 \\ \textless{}7-1> & \
\begin{tabular}{c} **constructed coarse** \\ \end{tabular} & 2.06 & 15.1 & 50.6 & 5.81 & 90 & 0.600 & 35.0 & 25.0 \\ \textless{}8-1> &
\begin{tabular}{c} **constructed coarse** \\ \end{tabular} & 2.57 & 13.6 & 60.3 & 5.91 & 92 & 0.900 & 250.0 & 28.0 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Table of geotechnical physical and mechanical parameters.  
Figure 1: Shield tunnel route map.