Compressed air process

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The compressed air process is a process that is used in tunnel construction when working in the groundwater as a measure for water retention and for temporary repair work on the face in shield driving . The process was first used in the 19th century.

Basics

When building a tunnel, it usually happens that you encounter mountain water when driving the tunnel . In order to keep the work area free from ingress of water, it is possible to press compressed air into the work area in order to force the water back again. The overpressure of the compressed air must be as high as the hydrostatic pressure of the water. Since the air pressure of the compressed air cannot be selected to be unlimited, this method is not suitable for all tunneling work. The level of usable air pressure is limited by the resilience of the human organism. The pressure currently permitted without a special permit, at which people may still be employed, is 3.6 bar in accordance with the compressed air ordinance . With a special permit, drives with an overpressure of up to 4.5 bar have already been created. The method is mainly used in tunnel construction in loose rock such as sand and silt areas.

history

Already at the beginning of the 19th century, when water burst in during the construction of the tunnel to cross under the Thames , the scientist Calladron made the proposal to use compressed air to keep water in the tunnel, but this was rejected. It was not until 1879 that the compressed air method was used for the first time in tunnel construction in Antwerp . In 1886 the method was used in London for a tunnel drive in combination with a shield drive by the engineer Greathead. Between 1892 and 1897, the Blackwall Tunnel , then the longest tunnel in the world, was excavated using the compressed air process . Between 1907 and 1911, the Sankt Pauli Elbe tunnel was the first underwater tunnel on the European continent to be excavated using this method . Compressed air shield tunneling was also tunnel in the greater New York City used where roads under the Hudson River and the East River were passed to Manhattan connect with the surrounding area to. Between 1903 and 1933 13 two-, three- and four-tube underwater tunnels were built that are still in use today.

Today, the process is usually only used for relatively short tunnels or for temporary repair measures in shield driving.

The procedure

Cutaway model of a compressed air shield seen from the chest. On the right the pressure-tight material lock. (ca 1910)

The method can be used in shield jacking , pipe jacking , shotcrete construction and cover construction . An important prerequisite for using the method is that the work area in the tunnel is hermetically sealed off from the rest of the tunnel area so that no compressed air can escape. In order to avoid compressed air losses, the top layer must also be as impermeable to air as possible, since otherwise additional measures such as artificial soil compaction would have to be used. The work area is separated from the rest of the tunnel area by means of a pressure bulkhead. Personnel and material locks, which must comply with the compressed air ordinance, are integrated into this pressure bulkhead, so that access to, supply and disposal of the work area is possible without major compressed air losses. The work area is pressurized with compressed air, a compressor is required for this. The air requirement must be determined in advance in order to dimension the necessary technical systems accordingly. The compressed air is blown into the work area through the pressure bulkhead. The size of the pressurized work space is different depending on the work process and can, for. B. be limited to a small area in front of the tunneling machine when driving shields. The air pressure in the pressure range is constantly monitored by sensors and, if necessary, adjusted to the target value.

Occupational safety and hazards

Working under compressed air is associated with particular dangers. This is because compressed air is a relatively dangerous medium. First of all, the work stresses the organism in the area under compressed air more than work under normal atmosphere. For this reason, before entering the compressed air area, people must be gradually accustomed to the pressure by means of a pressure lock and, after leaving, accustomed to the normal air pressure in a decompression chamber . In addition, before they are allowed to work in pressure areas, all persons must undergo a medical test with which their suitability for compressed air is examined by an occupational physician. The increased oxygen content in the compressed air can encourage a fire. In addition, the increased oxygen content accelerates the spread of the fire. Furthermore, no explosive atmosphere may arise in the compressed air area. The explosion protection rules apply here. To be on the safe side, no easily flammable material may lie around unprotected in the airlock and such substances must be avoided as far as possible in the pressure area. The use of hazardous substances in the compressed air areas must be particularly monitored; they must be recorded as close as possible to the point of use. Otherwise, the regulations of the technical rules for hazardous substances (TRGS 900) apply . Special care must be taken with welding and burning work .

literature

  • Bertram Henry Majendie Hewett, Sigvald Johannesson and others: Shield and compressed air tunneling . McGraw-Hill, New York 1922 (English, archive.org ).

Web links

Commons : Compressed air tunneling  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b Gerhard Girmscheid: construction processes and methods of tunneling. 3rd revised and expanded edition, Verlag Ernst & Sohn, Berlin 2013, ISBN 978-3-433-03047-9 , pp. 304, 520-522.
  2. ↑ a b Florian Köppl: Extraction tool wear and empirical wear forecast when driving with hydroshield TBM in loose rock. Approved dissertation at the Chair of Engineering Geology at the Technical University of Munich, Munich 2014, pp. 1–2.
  3. ↑ a b c d e f Dimitrios Kolymbas: Geotechnical tunnel construction and tunnel mechanics . Springer Verlag, Berlin Heidelberg New York 1998, ISBN 978-3-540-62805-7 , pp. 107-111.
  4. ↑ a b c d e f g h i j k 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
  5. ^ A b c d e Philipp Kohlschreiber: Overprint under Lucerne. In: Tec21. No. 49–50, Volume 136, ETH Library, Zurich 2010, pp. 23–25.
  6. ↑ a b c Kölner Verkehrs-Betriebe-AG (Ed.): North-South Stadtbahn Cologne, tunnel construction with compressed air. Cologne, pp. 9-23.
  7. ^ Alan Howard, Brett Campbell, Derek Penrice, Matthew Preedy, Jim Rush: North American Tunneling 2018 Proceedings . Society for Mining, Metallurgy & Exploration, 2018, ISBN 978-0-87335-466-0 , pp. 933 ( google.cz [accessed February 29, 2020]).
  8. ↑ Gerhard Girmscheid: Construction and construction in tunnel construction. 2nd edition, Verlag Ernst & Sohn, Berlin 2008, ISBN 978-3-433-01852-1 , pp. 290, 301-307, 471-473.
  9. ↑ K. Széchy: tunneling. Springer-Verlag, Vienna 1969, pp. 618-620, 652, 685, 714, 715.
  10. ^ A b c Professional Association for Health Services and Welfare Care BGW (Ed.): BGV C22 Accident Prevention Regulations for Construction Work. Version from January 1, 1997, fourth addendum, updated version, Druck Druckhaus Dresden GmbH, Dresden 2005, pp. 47–50.