# Model Test on the Behaviors of Deep Excavation with Lateral Confined Water
## 1 Introduction
### Model Test System and Materials  
The schematic of the model testing system is shown in Figure 2. The length, width and height of the model box are 2500, 2000 and 1500 mm, respectively. The side panels of the model box are made of 15 mm-thick tempered glass, which allows for the observation of the changes within the excavation. The base is constructed from 5 mm-thick steel plates, ensuring the rigidity of the structure. Water inlets are reserved in the middle of the long sides of the box bottom, which can be used for the arrangement of the water supply network and water level monitoring. The geometric similarity ratio \(L\) selected in this study is \(1/80\) (i.e., \(N=80\)). Based on the foundation pit project in a confined aquifer in Hangzhou, as well as Table 1, the soil layers in the model (from top to bottom) consist of a 250 mm-thick clay layer, a 100 mm-thick fine sand layer (representing the confined aquifer), a 100 mm-thick clay layer, and a 950 mm-thick fine sand layer. The model excavation has a length of 2500 mm, a width of 300 mm, and a depth of 300 mm. The depth of the diaphragm wall is 540 mm, and its insertion ratio (ratio of the diaphragm wall length below the excavation floor to the excavation depth) is 0.8. The model includes five horizontal struts with 500 mm spacing, and four vertical struts with vertical spacings of 95 mm, 95 mm, and 70 mm from top to bottom. As this explorative study focuses on the behaviors of a foundation pit subjected to lateral confined water, rather than predicting the actual stress and deformation of the  
Figure 2: Schematic of model test system: (a) cross-sectional view; (b) plan view (unit: mm). prototype, the clay and fine sand excavated from the excavation project in Hangzhou was adopted as the model soil. Thus, the soil similarity is not considered in this study. The physical and mechanical properties of the model soil are shown in Table 2.  
Based on the anti-inrushing stability check for confined water pressure [16], the anti-inrush safety factor \(F_{s}\) (Equation (1)) was taken as 1.2 and 1.1, respectively. These values were used to determine the corresponding lateral confined water level \(h\) in the model test, which was 396 mm and 432 mm, respectively. \[F_{s}=\frac{\gamma_{\mathrm{m}}H}{\gamma_{\mathrm{w}}h} \tag{1}\]  
where \(F_{s}\) is the anti-inrush safety factor; \(\gamma_{\mathrm{m}}\) (kN/m\({}^{3}\)) and \(H\) (m) are the unit weight and thickness of the aquitard layers above the artesian water, respectively; \(\gamma_{\mathrm{w}}\) (kN/m\({}^{3}\)) is the unit weight of water; \(h\) (m) is the water head of the artesian water. The diaphragm wall for the model test was constructed using aluminum alloy panels (Figure 3), with an elastic modulus of 70 GPa, a Poisson ratio of 0.3, a thickness of 2 mm, a depth of 540 mm, and a length of 2500 mm. The bending stiffness of the model diaphragm wall was calculated based on the thin plate theory, yielding a value of 5.128 \(\times\) 10\({}^{-5}\) kN\(\cdot\)m. This was compared to the prototype diaphragm wall bending stiffness of 2.604 \(\times\) 10\({}^{3}\) kN\(\cdot\)m, which satisfies the geometric similarity. The struts for the model test were made from aluminum alloy tubes (Figure 4), with an elastic modulus of 70 GPa, a Poisson ratio of 0.3, and inner and outer diameters of 8 mm and 12 mm, respectively, with a length of 300 mm. The compressive stiffness of the struts was calculated based on axial compression, yielding a value of 4.398 \(\times\) 10\({}^{3}\) kN. This value was compared to the compressive stiffness of the prototype struts, 2.263 \(\times\) 10\({}^{9}\) kN, which also adheres to the geometric similarity. Each strut consists of three components (Figure 4a): an aluminum alloy long tube, an aluminum alloy short tube, and an aluminum alloy screw rod. Both ends of the long and short tubes are threaded and connected via the screw rod, which allows for the adjustment of the overall strut length to its minimum.