Tunnel construction
The interior of Canary Wharf station has been likened to an underground cathedral, owing to the sheer size of the excavation.
This, and the availability of electric traction, brought about London Underground's switch to bored tunnels at a deeper level towards the end of the 19th century.
In certain predominantly urban applications, tunnel boring is viewed as quick and cost effective alternative to laying surface rails and roads.
Some types of TBMs, the bentonite slurry and earth-pressure balance machines, have pressurised compartments at the front end, allowing them to be used in difficult conditions below the water table.
This requires special precautions, such as local ground treatment or halting the TBM at a position free from water.
In February 2010, Aker Wirth delivered a TBM to Switzerland, for the expansion of the Linth–Limmern Power Stations located south of Linthal in the canton of Glarus.
[5] This in turn was superseded by the Madrid M30 ringroad, Spain, and the Chong Ming tunnels in Shanghai, China.
As of January 2023[update], the largest TBM by head diameter ever built was the Tuen Mun–Chek Lap Kok TBM, a 17.6-metre (58 ft) diameter machine built by Herrenknecht, for the Tuen Mun-Chek Lap Kok Link in Hong Kong.
[6] Clay-kicking is a specialised method developed in the United Kingdom of digging tunnels in strong clay-based soil 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.
During the First World War, the system was used by Royal Engineer tunnelling companies to put mines beneath the German Empire lines.
By special monitoring the NATM method is flexible, even at surprising changes of the geomechanical rock consistency during the tunneling work.
Tunnels constructed by pipe jacking are normally small diameter bores with a maximum size of around 3.2 metres (10 ft).
The 126m long 20m clear span underpass below the high speed rail lines at Cliffsend in Kent, UK.
[10] During construction of a tunnel it is often convenient to install a temporary railway, particularly to remove excavated spoil, often narrow gauge so that it can be double track to allow the operation of empty and loaded trains at the same time.
