- Sections of tunnels: advantages, limitations and suitability of each section
- Shaft, pilot tunnel.
- Driving tunnel in rocks, sequence of construction operations
- Full face method, heading and bench method, drift method
- Driving tunnels in soft ground, sequence of construction operations, needle beam method
- Shield tunneling, compressed air tunneling.
- Sections of tunnels, suitability of each section:
- Circular shaped tunnels
- Horse-Shoe shape tunnels
- Vertical walls with arched roof(D-Shaped tunnels).
- Shaft, Pilot Tunnel:
- It helps in providing proper ventilation to the main tunnel.
- It helps in removing the muck from the main tunnel quickly.
- It helps in providing proper lighting in the main tunnel.
- Driving Tunnel in rocks, sequence of construction operations:
- Setting up and drilling
- Loading holes with explosives and firing them.
- Ventilation and removing the dust after the explosion.
- Loading and hauling muck.
- Removing the ground water if necessity arises.
- Erecting supports for sides and roofs in necessity arises.
- Placing reinforcement.
- Placing concrete lining.
- Tunneling in hard rocks
- Tunneling in soft rocks.
- Full face method
- Heading and benching method
- Drift Method
- Pilot tunnel method
- Perimeter method
- Full Face Method
- Heading and Benching Method
|Heading and Benching Method (Tunneling)|
- Drift Method:
|Drift Method (tunneling)|
- Needle beam method, sequence of construction operations
- Sequence of Working:
- First of all a small drift of size of about 1*1 m is prepared on the working face of the tunnel.
- The needle beam consisting of two I girders, bolted together with a wooden block at the center, is inserted in the drift and its roof is supported on lagging carried on the wooden segment as shown in the figure below. These segments are supported by jacks resting on the needle beam.
Needle beam method- 1
- As shown in the figure below, the needle beam is placed horizontally, whose front end rests on the drift itself and the rear end is supported on the vertical stout post, resting on the lining of the tunnel.
Needle beam -2
- The jack is placed on the top of the beam(Needle Beam) to support the roof with lagging and then drift is widened side ways and the whole section is excavated. After excavating lining may be provided.
- Compressed Air Tunneling Method:
Usually air is used in conjunction with a shield and air-tight locks. However, numerous small tunnels have been driven using only linear plates or wood cants only. This method can be safely adopted if the air pressure is approximately 1 kg/cm^2. If the pressure is more than 1 kg/cm^2, the working hours should be reduced considerably which will increase the cost of tunneling.
- The earth pressure varies from the top of the tunnel to the bottom of the tunnel.
- As the pressure in the floor of the tunnel depends upon the nature of the strata, it is difficult to ascertain it theoretically.
- The value of pressure varies with the moisture content in different strata, which is difficult to ascertain.
- The compressed air will escape through the pores of the soil, hence air pressure will diminish continuously. Thus the value of air pressure will have to vary from time to time to get a balanced value and the determination of this value depends more on experience than theoretical considerations.