## 2 Test Design and Result Analysis
### Analysis of Monitoring Results
#### 2.3.1 Deformation of the Foundation Pit Retaining Structure  
It can be seen from the time-history curve shown in Figure 5 of the vertical displacement of the retaining pile top at typical positions ZTC-5, ZTC-9, ZTC-16 and ZTC-20 measuring points that the vertical displacement of the retaining pile top presents a floating trend in the excavation stage of the foundation pit. The main reason is that the foundation pit soil excavation is unloaded, and the bottom of the pit soil is uplifted and causes the pile to float. The maximum vertical displacement of the pile top of the retaining pile occurs at measuring point ZQC-16 (i.e., the position far from the station side), and the maximum vertical displacement is 2.1 mm. In the pouring stage of the bottom slab, the top of the retaining pile shows an obvious subsidence trend, mainly because the pouring of the bottom slab concrete is equivalent to the application of the load to inhibit the uplift of the foundation pit bottom, resulting in the downward settlement trend of the retaining pile. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Construction Phase (Excavation)** & **Construction Time** & **Construction Progress** & **Excavation Volume (m)** \\ \hline
1 & 15 November 2018\(-\)15 December 2018 & & 3.5 \\
2 & 15 December 2018\(-\)15 January 2019 & & 6 \\
3 & 15 January 2019\(-\)15 February 2019 & Earth excavation & 5 \\
4 & 15 February 2019\(-\)15 March 2019 & & 6 \\
5 & 15 March 2019\(-\)1 May 2019 & & 6 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Excavation time of each stage of the foundation pit. Figure 5: Time\(-\)history curve of the vertical displacement of the pile top of the retaining pile. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Project** & \multicolumn{2}{c}{**Scheduled Maintenance (mm)**} & \multicolumn{2}{c}{**Regular Maintenance (mm)**} \\ \cline{3-6}  & & **Main Line** & **Other Lines** & **Main Line** & **Other Lines** \\ \hline \multirow{6}{*}{Line tracks} & Gauge & +4, \(-\)2 & +5, \(-\)2 & +6, \(-\)3 & +7, \(-\)3 \\  & Level & 4 & 5 & 6 & 8 \\  & Height & 4 & 5 & 6 & 8 \\  & Rail direction & 4 & 5 & 6 & 8 \\  & (straight line) & & 4 & 5 & 6 & 8 \\  &
\begin{tabular}{c} Easement curve \\ Branch lines and \\ circular curves \\ \end{tabular} & 4 & 5 & 6 & 8 \\ \hline \hline \end{tabular} Note: 1 The gauge deviation does not contain the gauge widening value set according to regulations on the curve; however, the maximum gauge (including widening value and deviation) should not exceed 1456 mm. 2 The orbit deviation and height deviation are the maximum vector values measured by a 10 m chord. 3 The deviation of the triangle pit does not contain the distortion caused by the curve superelevation along the slope. When checking the triangle pit, the base length is 6.25 mm, but there is no triangle pit beyond the table within a distance of 18 m.  
\end{table} 
Table 3: The management values of the allowable deviation of the static geometric dimensions of the track. The measured horizontal displacement data of the four direction measuring points ZQS-3, ZQS-7, ZQS-17 and ZQS-20 of the retaining pile are selected for analysis, as shown in Figure 6. During the excavation and construction of the foundation pit in each stage, the horizontal deformation trend of the retaining pile top is toward the inner side of the foundation pit (the value toward the inner side of the foundation pit is positive, and the value toward the outer side of the foundation pit is negative), and it shows a continuous rise. The maximum horizontal displacement of the retaining pile top occurs at the ZQS-3 measuring point, which is 6.2 mm. In the floor pouring stage, the horizontal displacement of the retaining pile top has a sudden decrease trend, and the maximum change value reaches 3.5 mm. Horizontal displacement deformation gradually converges, which inhibits the drift of the retaining structure to the inside of the pit.