## 2 Monitoring Program and Result Analysis  
### Project Overview  
The road undercrossing a subway viaduct project utilizes pile foundation underpinning technology to create a deep foundation pit. This pit is divided into two sections, specifically the left and right sides. Figure 1 displays the plane diagram of the pile foundation underpinning project.  
To ensure the uninterrupted operation of the current subway system during the construction period, it is necessary to reinforce the pile foundations of sections 6#, 7#, 8#, 11#, and 12# before excavating the deep foundation pit for the road. Additionally, the existing foundation must be deepened and widened to allow for the smooth passage of the new road's deep foundation pit beneath the subway viaduct's foundation. This will ensure the safe operation of both the bridge and subway structures. Piers 8# to 11# support a continuous beam spanning a total length of 40.5 m + 50 m + 40.5 m in the upper section of the subway viaduct. The other piers hold simple-supported beams. Table 1 displays the summary table of the piling foundation for the piers of the current subway viaduct. The piers that require underpinning for piling foundations are 6-1#, 6-2#, 7-1#, 7-2#, 8-1#, 8-2#, 11-1#, 11-2#, 12-1#, and 12-2#. Additionally, the piers near the road foundation pit  
Figure 1: Schematic diagram of the pile foundation underpinning project.  
that needs underpinning are 5-1#, 5-2#, 9#, 10#, 13-1#, and 13-2#. The remaining piers are numbered 3#, 4#, 14#, 15#, and 16#.  
The schematic diagram of the underpinning structure is shown in Figure 2.  
The engineering geological conditions are as follows, which is shown in Figure 3. The surface layer along the proposed road is generally an artificial accumulation layer ranging from 0.50 m to 3.00 m thick, and the soil quality is mainly chalky soil and a vegetal fill 1 layer and miscellaneous fill 1 layer. There are recent sedimentary layers along the proposed road, and the soil quality is mainly a 2 layer of powdery clay, a 2 layer of chalk, a 2 layer of chalk, and a 2 layer of fine sand. Below the recent sedimentary layer is the Quaternary sedimentary layer, which is mainly composed of clayey soil, chalk, and sandy soil interaction layer, with rounded gravel and pebble soil layer in local distribution. Specifically, it includes the following: powdery clay 3 layer, chalk 3 layer, organic clay 3 layer, fine sand and medium sand 4 layers, powdery clay 5 layer, chalk 5 layer, fine sand, medium sand 5 layers, clay 5 layer and gravel 5 layer, fine sand and medium sand 6 layers, powdery clay 6 layer, clay 6 layer.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Pier Number**} & \multicolumn{2}{c}{**Diameter of the Pile**} & \multicolumn{2}{c}{**Length of the Pile**} & \multicolumn{2}{c}{**Number of the Pile**} \\  & **(m)** & **(m)** & **(Piece)** \\ \hline
3\# & & 30 & 4 \\
4\# & & 30 & 6 \\
5\# & & 30 & 6 \\
6\# & & 30 & 6 \\
7\# & & 30 & 6 \\
8\# & & 32 & 6 \\
9\# & & 35 & 9 \\
10\# & \(\phi\)1 & 35 & 9 \\
11\# & & 32 & 6 \\
12\# & & 30 & 6 \\
13\# & & 30 & 6 \\
14\# & & 30 & 4 \\
15\# & & 30 & 4 \\
16\# & & 30 & 4 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Summary of pier pile foundations of existing subway viaducts.  
Figure 2: Schematic diagram of the underpinning structure.  
The groundwater level investigation of the project is shown in Table 2.  
The foundation hole requiring underpinning for the abutment is located outside the groundwater area. The lower slab of the road's deep foundation hole is situated beneath the level of groundwater. Due to the high water head of the limited area and the presence of an existing subway viaduct, dewatering procedures cannot be implemented for the deep foundation pit of the road undercrossing. Therefore, it is necessary to implement appropriate water-stopping measures.