Urban tunnels

Underground tunnel construction in urban areas is generally carried out using the shield tunneling method. This method uses a large metal cylinder with a cutting wheel (tunnel boring machine) that slowly rotates to carry out excavation. The method enables safe tunnel construction even through ground beneath developed / urban areas and ground with a high groundwater level, e.g. underneath a river. The shield tunneling method is primarily used for tunnel construction of the Chuo Shinkansen in urban areas.

Construction procedures

Construction begins with boring a vertical pit to set up the starting base for a tunneling shield. The shield machine is then carried in through the pit and assembled before commencing excavation in the horizontal direction. The pit is later used for emergency access.

There are two ways to bore a vertical pit. One is the “diaphragm wall construction” method of building a continuous reinforced-concrete wall, and the other is the "pneumatic caisson" method, typically adopted when the groundwater level is relatively high. Both of the methods are very safe, with extensive track records in urban areas. In the Chuo Shinkansen project, JR Central will use the method suitable for each of the construction sites to ensure safety.

Boring a vertical pit emergency access

Bore a vertical pit that will be used for emergency access.
The excavation work may be carried out using the “diaphragm wall construction” method or "pneumatic caisson" method.

'Diaphragm wall' construction method

Video description of the two pit (emergency access) excavation methods

Pneumatic Caisson Method to Build Emergency Access in Urban Areas

Diaphragm Wall Construction Method to Build Emergency Access in Urban Areas

Excavating an underground tunnel

Use a tunneling shield to drill a tunnel between two vertical pits used for emergency access.

Video description of the shield tunneling method

Excavation by the Shield Tunneling Method