## 3 Simulation of Water Intrusion into Subway Station Operating Conditions
### Total Water Accumulation and Drainage in Subway Stations  
In the event of a simulated high water level intrusion occurring in reality, the subsequent flood drainage at subway stations is of greater consequence than the evacuation of passengers. In order to ascertain the subsequent drainage measures, it is first necessary to determine the quantity of accumulated water in the subway station as a result of flooding. By integrating the time using the \"D-value\" mass flow rate presented in Figure 9a-c, it is possible to ascertain the total accumulated water volume within the station. The volume of accumulated water in a subway station is determined by the area enclosed by the mass flow rate curve and the time axis, representing the difference between flood inflow and outflow. In the calculation, the composite trapezoidal integral was employed. The cumulative volume of floodwater in the subway station under the three working conditions is calculated to be 9301 m\({}^{3}\), 11,779 m\({}^{3}\), and 15,239 m\({}^{3}\), as illustrated in Table 4. The lack of comprehensive data precludes the establishment of a definitive numerical correlation between the accumulated water volume within the subway station and the flood height. Nevertheless, it can be discerned that as the height of the floodwater outside the station rises, the volume of accumulated water inside the station will correspondingly increase. In the event of the station being drained, the ingress of floodwater at the level of the flood invasion presents a significant risk to the safety of the personnel on site. Accordingly, the objective of the drainage design is to prevent flooding of the station, with the accumulated flood inside the station considered a fixed value. It is assumed that the flood will not flow into the tunnel through the station, and that the water in the tunnel will not flow back into the station during the pumping process. The pumping time is typically measured in hours (h), whereas the water flow inside the station changes rapidly, often in seconds (s). In the absence of new inflow, the accumulated water in the station hall level will inevitably flow into the platform level over time. If the space occupied by the stairs is not taken into account, the space available for fluid flow on the platform floor is approximately 17,610 m\({}^{3}\), which is sufficient to accommodate all accumulated flooding within the subway station. Industrial water pumps can be classified into the following categories according to their intended function: clean water pumps, hot water pumps, corrosion-resistant pumps, oil pumps, sewage pumps, impurity slurry pumps, submersible pumps, vacuum pumps, and specialised pumps. In light of the heterogeneous nature of the flooding within a station, comprising a mixture of water and sedimentary materials, it is evident that the most appropriate pumping apparatus would be a sewage pump, given that its primary function is to remove water from a given environment. The QW (WQ) type non-clogging submersible sewage pump exhibits a number of advantageous characteristics, including a compact overall structure, a relatively small volume, low noise levels, a significant energy-saving effect, convenient maintenance, the ability to operate without the necessity of constructing a pump room, and the capacity to function by diving into the water, which greatly reduces engineering costs. In the event of flooding within a subway station, this type of sewage pump can be utilised as a pumping facility. In the process of pumping water, the sewage pump is situated within the tunnel and pumped directly from the tunnel, resulting in an actual head of 14.75 m. When selecting a specific model, it is recommended to choose a submersible sewage pump with a head that is slightly higher than the actual head. Consequently, in light of the considerable accumulation of floods, it is imperative to select submersible sewage pumps with enhanced power and calibre.