• Concrete lining is one of the most conventional type of lining which has successfully been used in India and other parts of the world.
  • After excavating the tunnel, it is required to be lined with concrete.
  • The lining is done in two or three parts.i.e overt, invert and kerb.
  • For lining of overt of the tunnel, travelling type of shutter forms of suitable length are used.
  • In tunnels to be used for water, concrete lining is done to prevent seepage of water.
  • For tunnels to be used in traffic, concreting is done in portions where rock formation needs additional support.
  • Cement concrete lining eliminates weed growth and thereby improves flow characteristics.
  • Provision of concrete lining reduces maintenance charges to a minimum.
  • Cement concrete lining without reinforcement may be damaged due to excessive external water pressure.
  • The reinforced concrete lining can withstand the external water pressure but at a very high cost.
  • When unexpected water pressures are encountered, un-reinforced lining will crack more easily than the reinforced lining and will relieve the pressure thereby reducing the area of damage.

Tunnel concreting includes:

• Placing of reinforcement
• Fixing of formwork
• Supplying mixed concrete to the place of use in tunnel.
• Placing the concrete and compacting it after placement.

1. Reinforcement steel is bend to the required shape in the bending workshop and transported to the tunnel in sections and then assembled inside the tunnel.
2. Steel ribs, bars etc are used for thick concrete lining.
3. Form-work for the tunnel is made up of steel or wood or combination of both.
4. The form should be designed so as to resist the pressure of the concrete during its placement.
5. Concrete mix is produced in the mixing plant outside the tunnel and transported in transit mixtures, agitator mixers or dump trucks to the tunnel concreting site.
6. The forms are placed and fixed in position and then the concrete is forced into the form-work by using concrete pump or pneumatic concrete placer.