Tunnel construction by means of TBM
The key element of the tunnel construction shield technology is header, mobile cylindrical-shell-shaped temporary tunnel support allowing performing the necessary heading operations: ground cutting and loading, ground transportation, lining construction. Ground excavation is performed in the head part of the machine; lining is performed in tail of the shield.
Tunneling shields can be divided into 2 categories:
- Large - 8.5 - 9.75 m
- Medium - 5.7 - 6.7 m
- Small - 2.6 - 3.6 m
- Without face diaphragm
- With baffles
- With face diaphragm
- With hermetic protection enclosure
Sphere of use:
- Unstable ground
- Weakly-stable ground
- Stable ground of various hardness
The main sizes of tunneling shields depend on lining diameter, geological conditions and type of mechanized equipment. The heading speed depends on cross-section and type of tunneling shield; and when there are favourable conditions it can reach several metres per month. The constructions of tunneling shields are improved by means of unified cutting tools and loading buckets, spare parts development.
Mechanized tunneling shield is equipped with working attachment which helps ground cutting, transporting by means of drag head and loading in the means of transport. Shield moving is performed with face development. When the shield is moved to the distance of circle of lining, another circle is raised. So the working cycle is repeated permanently: ground excavation - ground transportation - lining. Special mechanism - erector arm tunnel driver - is applied for lining construction.
From the point of construction the shield is a metal shell consisting of 3 main parts. The front part with cutting tools works directly with face. In the central part there are adjustable jacks for shield moving along the perimeter of the shield. The tail of the shield is a cylindrical shell where another lining circle is raised. The lining construction is accompanied with veneer wall tie grouting which helps fill space between lining and ground surface.
* Tunneling shield was first used by M. Brunel in Great Britain for tunnel construction under Themes (1825). Tunnel shields have been applied in USSR only since 1932. By means of these machines vast majority of subway tunnels in Moscow, St-Petersburg and other cities were constructed.
The world record of heading speed - 1250 metres of tunnel per month - was set in 1981 with shield KT-1-5.6 on the section of Pionerskaya-Udelnaya of main line tunnel of St-Petersburg subway. In 70s and 80s these shields were considered to be the better ones in the world.