Dewatering (tunnel construction)

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In tunnel construction, dewatering is the term used to describe all measures that serve to safely keep the mountain water away, to collect and safely drain away all water. The dewatering for a tunnel must be coordinated with the construction phase and the operating time of the tunnel.

Basics

When building a tunnel, it must be taken into account that mountain water is usually encountered when driving the tunnel. The amount of water encountered can be considerable, especially if water-filled cavities are approached during the excavation. This can lead to flooding of the tunneling area. The hydrological conditions must be clarified in the run-up to the construction phase by means of a corresponding expert opinion. So it is clarified in advance what amounts of mountain water can be expected and in which areas larger amounts of mountain water occur. In addition, the composition of the mountain water can be clarified in advance. In particular, it must be clarified where the water comes from and what effects it has on the surface. There is water that contains harmful minerals or has a pH value that can damage the concrete of the tunnel lining. It has to be clarified whether the water can be used for other purposes and how it can be returned to nature. The necessary dewatering measures can be planned on the basis of the report. It is important to ensure that as little water as possible is withdrawn from the mountains for ecological reasons.

Measures (construction phase)

The dewatering can be done in four ways when building a tunnel. In this way, the water can either be diverted, displaced, shut off or lowered.

Water drainage

When draining the water, it must be ensured that, in addition to the mountain water, there is also process water and day water. The resulting mountain water is if possible in the tunnel reveal through suitable measures such. B. the building drainage taken and discharged via water pipes. If the tunnel rises slightly, the water can drain off naturally. If the tunnel slopes down, the water must be collected in a pump sump and pumped out of the tunnel. The resulting water (mountain water, surface water, process water) can either be collected in mixed systems or in separate systems and discharged through separate pipelines. Contaminated water has to undergo a cleaning process outside the tunnel and be treated before it is returned to nature.

Displacement

The water displacement is a process that is mainly used in underground railway construction in loose rock. The working area of ​​the tunnel is pressurized using compressed air. The overpressure must be as high as the water pressure at the tunnel bottom. This prevents the water from entering the tunnel area. The process that is used here is the compressed air process .

Water shut-off

Appropriate measures can be used to prevent mountain water from entering the tunnel. Depending on the design of the tunnel, slotted, narrow, sheet pile or bored pile walls can be built into the groundwater retaining layer from the surface . There is also the option of preventing the water from entering through injections, jet grouting - columns or through freezing processes . In order to prevent water from entering the tunnel in the long term, it is necessary to cover the entire tunnel extension with sealing sheeting. There are different systems for this.

Water lowering

This form of dewatering is known as closed dewatering. Here, before the tunnel is driven, the water is lowered using measures such as gravitational wells, vacuum wells or electroosmosis .

Measures (operating time)

Suitable measures must be taken to ensure that the mountain water cannot penetrate the tunnel when it is in operation. For this purpose, sealing foils are placed around the segments during the construction phase and embedded in concrete or, in the case of a two-shell construction, integrated into the space between the two-shell construction. As a rule, the sealing measures result in only relatively small amounts of water from the roadways, which are drained off via the sewerage system of the roadway drainage system. Another form of dewatering is to collect the mountain water through drainage pipes in the area of ​​the roof and to lead it out of the tunnel via a drainage system. As a rule, the water from the roadway drainage and the mountain water are drained from the tunnel via a common drainage system. If necessary, the tunnel water is cleaned accordingly outside the tunnel and only then fed into the receiving water. Depending on the composition of the mountain water, deposits can form in the drainage pipes, which reduces the function of the drainage.

Individual evidence

  1. ↑ a b c d Christian Amstad, Kalman Kovari: Underground construction in swellable rock. Institute for Geotechnical Engineering of the Swiss Federal Institute of Technology Zurich, Zurich 2001, research assignment 52/94, pp. 131–169.
  2. ↑ Petra Panova: Resource requirements of inner-city subway construction. Master's thesis at the Vienna University of Technology, Vienna 2014, pp. 38–43.
  3. ↑ a b c d e f g Federal Highway Research Institute (Hrsg.): Guideline for mountain water drainage systems in road tunnels. RI-BWD-TU, December 2007 edition, pp. 5–14.
  4. ↑ a b c Walter Zanoskar: Gallery and tunnel construction. An introduction to the practice of modern rock cave construction, second revised edition, Springer-Verlag, Vienna 1964, pp. 122–130, 156.
  5. ^ Romedius Riedler: Tunnel construction in the Karst using the example of the Steinbühl tunnel. Master's thesis at the Chair for Subsurface Engineering at the Montan University Leoben, Leoben 2018, pp. 45, 46.
  6. ↑ a b c P. Reichl, G. Domberger, Ch. Reszler, G. Winkler: Hydrological investigations in tunnel construction - a synopsis of the variety of different questions and investigation methods . In: Contributions to hydrology. 2016, ISSN 0376-4826, pp. 73-82.
  7. ↑ a b Frank Abel: Use of the observation method to optimize tunnel drainage systems. Approved dissertation at the Faculty of Civil Engineering of the Ruhr University Bochum, Bochum 2003, pp. 42–53.
  8. ↑ Volker Wetzig: Tunnel water and chemistry. In: Tunneling. No. 29, Volume 114, ETH Library, Zurich 1996, pp. 630, 631.
  9. ↑ a b Dimitrios Kolymbas: Geotechnics - tunnel construction and tunnel mechanics . Springer Verlag, Berlin / Heidelberg 1998, ISBN 978-3-642-63752-0 , p. 16.
  10. ↑ Hagen Peters: Treatment of wastewater during the construction of the Gotthard Base Tunnel. In: bbr. No. 10, 2005, pp. 42-53.
  11. ↑ Bernhard Maidl, Martin Herrenknecht, Ulrich Maidl, Gerhard Wehrmeyer: Machine tunneling in shield driving. 2nd completely revised and expanded edition, Verlag Ernst & Sohn, Berlin 2011, ISBN 978-3-4330-2948-0 , pp. 217–227
  12. ↑ a b K. Szechy: Tunnel construction. Springer-Verlag, Vienna 1969, pp. 222-225, 428-431.
  13. ^ A b Jan Dirk Chabot, Michael Rehbock-Sander: Drainage of mining tunnels - new tendencies. In: Tunneling. No. 129, Volume 118, ETH Library, Zurich 2000, pp. 244–249.