Evaluation of Waterlogging Risk in an Urban Subway Station

Table 1

List of influence factors for evaluation of waterlogging risk in the urban subway station.

No.	Influence factor	Description
	Surrounding terrain	(1) The factor of surrounding terrain of a station determines the direction of confluence and flow rate of rainwater, which may be the prerequisite for waterlogging.
		(2) It has effects in the construction and operation periods.
	River course	(1) The foundation pit of the subway station is unconnected with the surrounding rivers in the construction period, and rivers or other large ditches for draining flood are found in the surrounding of the subway station. On the whole, it can be regarded as a favorable factor for preventing waterlogging.
		(2) Internal drainage system has been connected to external municipal pipe network and rivers in the operating period of the station and is not isolated any more. For too high water level of rivers, the backward flow of water should be taken into account, which can exert adverse impacts.
	Drainage pipe network	(1) Standard, scale, and construction degree of drainage pipe network within a certain range around the subway station have important influences on waterlogging prevention in the subway station.
		(2) The location of the drainage pumping stations in the station relative to surrounding rainwater pipe networks or the mouth of a river should be considered. On extreme weather conditions, excessive rainwater accumulated in rainwater pipes can lead to water flowing backward, which exerts adverse effects.
	Municipal sewage and feed-water main pipes	(1) Municipal sewage and feed-water main pipes are extremely likely to burst in the construction period, and water in the pipes overflows after bursting of the pipes. Under the effects of pressured water flowing, soil layer of the wall of the foundation pit becomes unstable, collapsing foundation pit, which causes serious consequences.
		(2) By comprehensively considering accidental factors and the above reasons, municipal sewage and feed-water main pipes in the construction period are considered to be an adverse factor, which has great influences and hazards on the construction period. However, the probability of pipe bursting is greatly reduced in the operating period, so it has slight effects.
	Hydrogeological condition	(1) During the construction period, wall of the foundation pit plays a temporary role in seepage control and support and has a simple structure, so influence of hydrogeology is quite significant.
		(2) During the operating period, because a reliable structural antiseepage system has been formed in the station, the impacts of groundwater are basically eliminated and hydrogeological condition has little effect.
	Regional situation	(1) During the construction period, it is necessary to encircle the construction site and control the traffic around the construction site, which aggravates the original traffic and pedestrian flow and affects the surrounding important public facilities. Therefore, in comparison with the operating period, it has greater influences in the construction period.
		(2) Regional situation, such as the distance from the station to densely populated area, complete and smooth road networks around the station, and smooth allocation of emergency supplies can affect short-term and long-term planning for waterlogging prevention in the urban subway stations.