# Dewatering-Induced Stratified Settlement around Deep Excavation: Physical Model Study
## 3 Materials and Methods
### Underground Structure Model  
As the length similarity ratio \(\alpha_{L}\) = 150:1, the size of the deep excavation model can be calculated and shown in Table 4. The diaphragm wall of the deep excavation model is simulated by the PMMA tube, and the outer wall is rough polished to improve its waterproofing ability and friction. The planar multi-point uniform distribution method is used to simulate dewatering inside the deep excavation. The discharging wells are perforated steel pipes covered with 300-mesh gauze. In addition, the distribution under the collection device is uniform. Thus, groundwater can be centrally discharged with a constant flow by a peristaltic pump. Linear multi-point uniform distribution method is used to simulate groundwater recharging (spacing is 200.0 mm). Moreover, the recharging wells are set parallel to the tunnel model near the deep excavation model, and constant water pressure is used during the test. To analyze the dewatering-induced environmental impact around the deep excavation, the building models, tunnel model, and monitoring points for stratified settlement, groundwater level, and earth pressure are set around the deep excavation model (Figure 3). Three building models with end-bearing pile foundations are set beside the deep excavation model, and the actual piles are equivalently replaced with eight PMMA (polymethyl methacrylate) piles that are evenly distributed on the plane (spacing is 50.0 mm), with a diameter of 14.0 mm and a length of 360.0 mm. A 100.0 \(\times\) 200.0 \(\times\) 1.5 mm steel plate covers the PMMA piles to simulate the foundation slab, and a 25.0 kg weight is placed on it to simulate the building load. A single-track tunnel model is set beside the deep excavation model. It is simplified as a plastic-coated metal hose with an outer diameter of 51.0 mm in the physical model, and steel joints are set in the tunnel model every 300.0 mm to connect the settlement poles and the earth pressure sensors. The tunnel model was buried in layer 3 + 4 of mucky clay, and two 150.0 \(\times\) 150.0 \(\times\) 400.0 mm PMMA boxes are set at both ends to simulate the underground structures of the subway station. Compared with the prototype tunnel, the tunnel model has lower stiffness and larger deformation range, which are more conducive to the analysis of the deformation law. To avoid the influence of the sensor on soil deformation, small-sized sensors were selected. The size of the pore water pressure sensor is \(\varphi\) 1.0 cm and 2.0 cm in thickness, and the size of the earth pressure sensor is \(\varphi\) 2.5 cm and 0.5 cm in thickness. The settlement pole is made of a \(\varphi\) 0.2 cm pole and two 1.5 cm \(\times\) 1.5 cm plates at both ends, and a \(\varphi\) 0.3 cm sleeve was placed on the outside of the 0.2 cm pole, so it can move freely along the vertical. For the strata soil in the physical model, similar materials are filled from bottom to top in layers with a thickness of 50 mm. The underground structure model is pre-buried, and monitoring sensors are at an appropriate height. First, each layer of similar materials is compacted with a vibrating roller or a heavy hammer. Second, each layer is saturated with water from the bottom until the internal air is removed. To ensure that each layer of similar materials is uniform and meets the test design requirements, compacted samples of similar materials are collected for the density, water content, degree of consolidation, and hydraulic conductivity tests. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Category**} & \multicolumn{4}{c}{**Deep Excavation Model**} & \multicolumn{2}{c}{**Discharge/Recharge Well**} \\ \cline{2-7}  & **Inner Diameter** & **Thickness** & **Excavation Depth** & **Buried Depth** & **Well Screen Length** & **Outer Diameter with** \\  & & & & & **Sand Filter** \\ \hline Prototype (m) & 30.00 & 1.50 & 59.60 & 105.00 & 30.00 & 1.20 \\ Physical model (mm) & 200.00 & 10.00 & 400.00 & 700.00 & 200.00 & 8.00 \\ \hline \hline \end{tabular}
\end{table}