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There are a variety of TBM designs that can operate in a variety of conditions, from hard rock to soft water-bearing ground. Some TBMs, the bentonite slurry and earth-pressure balance types, have pressurized compartments at the front end, allowing them to be used in difficult conditions below the [[water table]]. This pressurizes the ground ahead of the TBM cutter head to balance the water pressure. The operators work in normal air pressure behind the pressurized compartment, but may occasionally have to enter that compartment to renew or repair the cutters. This requires special precautions, such as local ground treatment or halting the TBM at a position free from water. Despite these difficulties, TBMs are now preferred over the older method of tunnelling in compressed air, with an airlock/decompression chamber some way back from the TBM, which required operators to [[work in compressed air|work in high pressure]] and go through decompression procedures at the end of their shifts, much like [[underwater diving|deep-sea divers]].
In February 2010, Aker Wirth delivered a TBM to Switzerland, for the expansion of the [[Linth–Limmern Power Stations]] located south of [[Linthal, Glarus|Linthal]] in the [[canton of Glarus]]. The borehole has a diameter of {{convert|8.03|m|ft}}.<ref>{{cite web |title=Tunnels & Tunnelling International |url=http://www.tunnelsonline.info/story.asp?sectioncode=1&storycode=61846
=== Clay-kicking ===
Clay-kicking is a specialized method developed in the [[United Kingdom]] of digging tunnels in strong clay-based soil structures. Unlike previous manual methods of using [[mattock]]s which relied on the soil structure to be hard, clay-kicking was relatively silent and hence did not harm soft clay-based structures. The clay-kicker lies on a plank at a 45-degree angle away from the working face and inserts a tool with a cup-like rounded end with the feet. Turning the tool manually, the kicker extracts a section of soil, which is then placed on the waste extract.
Used in [[Victorian era|Victorian]] civil engineering, the method found favor in the renewal of Britain's ancient [[sewerage]] systems, by not having to remove all property or infrastructure to create a small tunnel system. During the [[First World War]], the system was used by [[Royal Engineer tunnelling companies]] to put mines beneath the [[German Empire]] lines. The method was virtually silent and so not susceptible to listening methods of detection.<ref>{{cite web |date=2009 |title=Tunnelling |url=http://tunnellersmemorial.com/Tunnelling.htm
=== Shafts ===
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