Earth Pressure Balance Shield

Earth pressure balance shield is another important type of tunneling machine. It is normally applied for varying soil compositions and is excellent for smaller work sites. Within shield, the cutter excavates the site through rotary motion. In the earth-pressure balance shield, the excavated soil balances the excavating front. All excavation takes place within a steel ring called the cutter bit. In the excavation chamber, the excavated soil is mixed with a conditioning agent. An excavated soil is carried to a conveyor belt through a screw conveyor. From here soil is taken to the slurryfying box, where it is mixed with water and is taken out of the tunnel by the dredging pumps.

The excavated soil is mixed with additives and kneaded forcibly with the kneading blades to improve its plastic fluidity and impermeability. In the cutter chamber the pressure of the excavated soil is increased to counterbalance the tunnel face earth pressure and the groundwater pressure. Tunnel face can be sustained by muddy soil pressure to minimize ground settlement.

Applications
The major applications of earth pressure balance shields are :

• For laying pipes for smaller areas.
• Used for laying cables to be used for various purposes.
• Excavation for drainage and municipal purposes.