Question

In compressed air tunnelling, the amount of air required per minute per m² of face Area is
1. 1 m³/min/m²
2. 6 m³/min/m²
3. 10 m³/min/m²
4. 20 m³/min/m²

Answer 1

Correct Answer - Option 2 : 6 m³/min/m²

Concept:

Compressed Air TBM:

• Air compressed TBMs are tunnel boring machines where compressed air is used to counteract the hydrostatic ground pressure exerted against the cutter head.
• These machines are especially suited for excavation in unstable soils i.e. soft rocks with the presence of water.
• These machines work on the principle that the rotating cutter head acts as the means of excavation whereas face support is ensured by compressed air at a sufficient level to balance the hydrostatic pressure of the ground.
• Debris is extracted from the pressurized excavation chamber using a ball valve-type rotary hopper.
• In compressed air tunneling, 6 m³/min/m² of the face area is required.

Tunnel Boring machine (TBM):

The following table shows the different types of TBMs:

Types of TBMs
Hard Rock TBMs	Soft Rock TBMs
1. Gripper TBM  2. Shield TBM	1. Mechanical Support TBM  2. Compressed Air TBM  3. Slurry Shield TBM  4. Earth Pressure Balanced TBM