How to build tunnels in densely populated areas?

(28-01-2022) In his PhD, Weixi Zhang made a comprehensive study of the mechanical behaviour of a fairly new kind of tunnel that is quasi-rectangular in shape and is suitable to be built in densely populated areas.

Due to the rapid progress of urbanisation, during the past two centuries engineers have built an increasing number of infrastructure works all over the world, including many tunnels. One of the most common types is the shield tunnel.

Most modern tunnels using the shield method are drilled tunnels; in the past, tunnels were also dug. They are usually designed with a circular cross-section for optimum mechanical behaviour. Due to the strong load-bearing capacity of the tunnel roof, these tunnels can cover various depths and soils. On the other hand, this method does not need to open the ground surface during its construction. Therefore, the shield method is preferably chosen for tunnels crossing cities or rivers, such as metro tunnels and channel tunnels

"However, as urban space becomes more densely built up, more and more urban infrastructures have to be constructed underground. The solution with two circular tunnels, one for each direction, takes more space than one quasi-rectangular tunnel, with two tracks in it," explains Weixi Zhang.

"Shield tunnels with special cross-section can be designed with a configuration that better suits the tunnel objectives, like making two-way transportation in one tunnel, so that the underground space in the city can be used more efficiently and the number of tunnel excavations or the impact on existing buildings can be reduced."

In 2016, the concept of a quasi-rectangular shield tunnel (QRST) was introduced in a metro project in the Chinese town Ningbo, to further reduce construction costs and better solve the problem of underground construction when crossing a dense urban area.

"However, there is no specific design standard for this type of tunnel. The calculation method for a special section shield tunnel is usually based on that for circular tunnels, but the applicability for the design of QRSTs has not been verified so far," says Weixi.

"Therefore, in my thesis, I carried out a comprehensive study of the mechanical behaviour of the QRSTs, including the new joint pattern for the lining segments, used in the tunnel, the calculation model, the pressure distribution on the outer surface and a parametric study," concludes Weixi. In the framework of this research project, original loading tests on full-scale tunnel rings were performed, as well as a unique measuring campagne in a real tunnel project.

Read a more detailed summary or the entire PhD

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PhD Title: Numerical and Experimental Analysis of the Mechanical Behaviour of Linings in Quasi-Rectangular Shield Tunnels

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Contact: Weixi Zhang, Wouter De Corte, Luc Taerwe

Weixi Zhang

Weixi Zhang was born in 1991 in Henan, China. He received his Master's degree in Architectural and Civil Engineering in 2017 at the College of Civil Engineering of Tongji University.

Since 2018, he has been working as a Ph.D. researcher at the Department of Structural Engineering and Building Materials of Ghent University with a CSC scholarship. His research aims to perform a comprehensive analysis of the mechanical behaviour of quasi-rectangular shield tunnels, which are a new type of special-section shield tunnels. The research content includes the rotational and shear behaviour of the special joint type used in the studied tunnel, the calculation model, the surrounding pressure distributions, and the related parametric analysis by experiments and numerical simulations. The research findings and methods are believed to provide a good reference for future studies related to other special-section shield tunnels.

Weixi is the first author of two peer-reviewed journal articles and two conference papers. During his time at Ghent University, he also cooperated in industry services and education activities, such as master students tutoring, bridge vibration monitoring and assistance in exams and conferences.

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Editor: Jeroen Ongenae - Final editing: Ilse Vercruysse - Illustrator: Roger Van Hecke