Lining of tunnel :

The term lining is used to indicate the finishing touch given to the cross section of tunnel.If the tunnel is passing through hard stratum, it may be left unlined.Lining may be of two types:

Temporary lining:

it is provided for supporting the roof and the walls of tunnel during construction.

Permanent lining:

it is provided in soft soil which is always liable to disintegrate.The ideal lining should be easy to maintain, economical, durable, simple to construct and stable.

The basic materials for tunnel lining construction are cast-in-place concrete, cast-in-place and prefabricated reinforced concrete, cast iron and steel. These materials are chosen according to conditions of construction area and tunnelling methods. The shape and size of lining are defined by size, depth and function of the tunnel and sort of take up load (rock pressure, hydrostatical pressure, traffic load, etc).Cast-in-place lining is mainly used for construction of tunnels with most complex structure and big cross-section. Precast lining is widely used for shield and erector- arm tunnelling, mainly in subway tunnels.

Ventilation means supply of air, light and keeping the level of noise to bearable to human beings.

Tunnels may require ventilation for a variety of reasons such as

To ensure an adequate air quality

to control the spread of smoke in case of fire

to reduce temperatures to acceptable limits.

The function of the ventilation relates to the type of tunnel.

1. Vehicular tunnels (road, rail and metro) generally require high air quality during normal operation and smoke control in case of fire

2. Cable tunnels require cooling, smoke control and a certain amount of air exchange.

3. Mine tunnels and station tunnels also require adequate ventilation for physiological, cooling and smoke control requirements.

The ventilation to be provided can be put under following two heads:

i. Temporary ventilation: when ventilation is to be provided only at the time of construction.

ii. Permanent ventilation: When ventilation isto be provided after the construction work is over, such ventilation system must be on permanent basis.