Tunnel Lining | Object/ Purpose of Tunnel | Types of Tunnel | Sequence of Tunnel

Tunnel lining

A layer of timber, iron, masonry, or concrete provided on the inside of the tunnel is known as lining. Lining of tunnel is provided to give final shape to the tunnel cross-section and to give strength to the sides and roof to prevent them from collapsing.

Object/ purpose of tunnel

1. It provides the correct, desired shape and cross section to the tunnel

2. It support the loosened rock pieces during blasting

3. It reduces the maintenance cost of the tunnel

4. It improves the appearance of the tunnel

5. It provides plain surface of the electrical fittings

6. It increase the structural strength of the soft places of the tunnel

Sequence of lining

The lining of a tunnel is done in following steps

1. In the first stage grunting is done to seal the water in rock tunnel

2. Concrete lining is done either in one attempt as in case of circular tunnel or by separately tackling the vest, the side wall, and the arch. For small tunnel that measures 1.2 to 3.0 m in diameter, the concrete lining can be provided by the hand placing method. In case of bigger tunnel, concrete pumps or pneumatic places are used for placing the concrete.

3. The concrete is curved to its maximum strength. If the humidity inside the tunnel is not sufficient, curving can be done by spraying water through perforated pipes

4. The different types of lining practices adopted by Indian Railway depending upon ground condition are depicted.