Describe with neat sketches tunnelling in rock by heading and benching method.

The different methods of tunneling in Hard rock are:

a) Full face heading method.

b) Heading & bench method

c) Drift method

d) Pilot tunnel method

The various stages in the construction of tunnel are:

• Setting up and drilling.
• Loading holes and firing the explosives.
• Ventilation and removing dust.
• Mucking.
• Removing ground water.
• Timbering if necessary.
• Grouting.
• Lining.

Heading and Bench method

• Tunnel cross section is divided into two parts, the top portion of the tunnel is known as the heading and the bottom portion as bench.

• Usually this method is adopted for railway tunnels.

• In this method of tunneling, top portion or heading will be about 3.70 to 9.6 m ahead of the bottom portion.

• In hard rock which may permit the roof to withstand without supports, the top heading generally is advanced by one round of bottom portion.

• If the rock is broken then heading may be driven well ahead of the
  bottom portion and after giving proper support to the roof, the bottom portion is completed.

• In hard rock the heading is bored first and the holes are driven for the bench portion at the same time as the removal of the muck.