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Tunnel Construction. Tunnels are dug in types of materials varying from soft clay to hard rock. The method of tunnel construction depends on such factors as the ground conditions, the ground water conditions, the length and diameter of the tunnel drive, the depth of the tunnel, the logistics of supporting the tunnel excavation, the final use and shape of the tunnel and appropriate risk management.
Cut-and-cover construction at Saint-Michel on Paris Métro Line 4 (c. 1910) Cut-and-cover is a simple method of construction for shallow tunnels where a trench is excavated and roofed over with an overhead support system strong enough to carry the load of what is to be built above the tunnel. [29] There are two basic forms of cut-and-cover ...
Deep level underground is construction that is 20 m (66 ft) or more below ground and not using the cut-and-cover method, especially train stations, air raid shelters and bunkers, and some tunnels and mines. Cut-and-cover is a simple method of construction for shallow tunnels where a trench is excavated and roofed over with an overhead support ...
When building an underground transportation system using tunnel boring machines (TBM), the station box can be built before or after the TBM goes through that area. If the station box is created after the TBM has passed through, the tunnel built by the TBM would be replaced by the station box.
Underground construction has a number of unique risks and challenges but shares a lot with traditional construction and mining. Underground construction workers often work under reduced light condition, in dangerous spaces, and are at a high risk of exposure to contaminants, fire, and explosions.
A slurry wall is a civil engineering technique used to build reinforced concrete walls in areas of soft earth close to open water, or with a high groundwater table. [1] This technique is typically used to build diaphragm (water-blocking) walls surrounding tunnels and open cuts, and to lay foundations .
The City Rail Link was constructed using both cut-and-cover and tunnel boring machine (TBM) methods depending on the location of construction. The ground through which the tunnels were built varies between rock and soft soil, and with a variation in depth to natural ground level of between 40 metres and 0 metres. [71]
There are 20 miles (32 km) of cut-and-cover tunnel and 93 miles (150 km) of tube tunnel, the other 55% of the system running above ground. [1] Trains generally run on the left-hand track, although in some places, for example the Central line east of St Paul's station, tunnels are dug one above each other. [6]