Typical case analysis of deep tunnel drainage system in urban area

Urban rainstorm-waterlogging events were becoming more common and more difficult to control in the past decade. With the inadequate capacity of urban drainage system and the low standards of drainage planning, it is urgent to reform and improve the original drainage system. However, due to the constraints of space conditions, construction costs, environment interference and some other factors, it is not easy to transform the original drainage system and the effect is not obvious. Urban deep tunnel drainage system is an important method to alleviate urban waterlogging, as well as the initial runoff pollution and overflow pollution. The research on urban deep tunnel drainage system is necessary and important, especially in rapid urbanizing countries like China. The preliminary planning and studies have been done in several cities in China with the aim of solving urban waterlogging problem by urban deep tunnel drainage system. This kind of system has already been applied maturely in many developed countries/cities, such as Singapore, Chicago, London and so on. These applications can provide many experiences and lessons for Chinese engineers and researchers. By introducing the work principle of urban deep tunnel drainage system and analyzing its design and uses at home and abroad, this review provides technical support of deep tunnel system to reduce pollution and waterlogging. From the typical cases investigated in this paper, they confirmed that the urban deep tunnel drainage system could play a multiple role in urban waterlogging control and reducing overflow pollution. For example, in London, Paris, Singapore, they are used for drainage and the pollution control of overflow; in Tokyo and Hongkong, they are used for urban waterlogging control; in Chicago they are used both for waterlogging control and overflow pollution control. Although the experience of foreign countries and cities can be used for a reference to the system’s development in China, it cannot be completely copied. Besides, this review paper also points out the direction and main goals for the future research on urban deep tunnel drainage system. There are four key problems analyzed on its development, which are involved in both technical problems and management approaches. Some achievements have been made in urban hydrological simulation and evaluation technology, but this kind of technology has just started and has not been widely used. Scheduling management and joint design with other projects like sewage treatment plant are other two important parts that are directly related to the normal operation and efficiency of the tunnel. And it still faces many of unavoidable technical problems such as geological problems, operation management problem, etc. The review has summarized the key issues for researchers to understand the principles, development status and key problems of urban deep tunnel drainage system. It has certain reference value not only to the planning/design of urban drainage system, but also to the construction of the Sponge city. In the serious situation of the urban waterlogging as well as the initial runoff pollution and overflow pollution, it can be conducted that the research of urban deep tunnel drainage system has urgent practical needs and broad application prospects in China. Moreover, how to combine the characteristics of each city and find property solutions to the key problems still need further study.