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  Monolithic tunneling since 1988

  ABSTRACT: Independent on the location of a tunnel, country-side or submersed, watertightness is the main challenge for almost every tunnel. During the years solutions for tunnels have been developed in the construction and formwork business. It was always the goal to improve formwork systems and construction methods for higher quality of the tunnel, improvement of sustainability under consideration of reduction of labourtime (forming times) and resources. Depending on the size, location and length of the tunnel it is important to find the most economical solution for the construction-sequence and the formwork, also considering environmental-requirements and health and safety aspects. The first monolithic tunnels and sewage-water-canals have been designed and built with sealing-methods for horizontal and vertical construction joints. Therefore, companies like Trelleborg developed rubber sealing-systems for intermediate and permanent waterproofing, which is not part of the presentation. For the formwork, the form ties at external walls are the challenge to achieve watertightness. Lost ties with water stop have been the solution for many years, which did not fully satisfy. For the Öresund tunnel first time a new system with watertight concrete cones and special 2-component-glue was developed as a 100 %solution. These tie-systems are quite expensive in costs for material and labor, so in the following years we had the goal to reduce the number of ties as much as possible. After experience of Öresund and other projects the idea was to eliminate the ties at the external walls completely. This came up in 2010 when we started design studies for the Fehmarn-Belt-Tunnel. We came to a solution for immersed tunnels in monolithic casting by using retaining walls to support the concrete pressure at the external walls and eliminate the ties at the external walls. The first pour without ties was made at the HZMB-Tunnel in 2012. During the project it was also possible to reduce the ties at the internal walls, to save material and labour-time. With this experience we developed the solution, which now will be used for the Fehmarn-Belt-Tunnel, too.

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