Earth Pressure Tunnel Boring Machine (EPBTBM)

Definition - What does Earth Pressure Tunnel Boring Machine (EPBTBM) mean?

An earth pressure tunnel boring machine (EPBTBM) is a type of underground excavator that uses mechanical pressure at the face of the tunnel to counterbalance earth pressures. It is a form of tunnel boring machine that negates the need for compressed air to control subsidence of the tunnel face. In that sense, it has revolutionized soft-ground tunneling and become a prevalent tunneling method in high-traffic areas.

Trenchlesspedia explains Earth Pressure Tunnel Boring Machine (EPBTBM)

The selection of a tunnel boring machine (TBM) for a particular job is dependent on the type of soil being bored. An earth pressure balanced (EPB) machine is the first choice in homogenous, cohesive soils. With an EPBTBM, the extracted soil itself acts as a supporting medium for the machine. Conditioning agents are injected into the soil to make it more suitable to the task. The balance of the shield is controlled by the careful coordination of the advancement speed and the speed of the excavating screw.

Tunneling shields are nothing new. The first use of the technology was by Marc Isambard Brunel in 1818. He used the method to create a tunnel under the Thames River. An advancement known as the Greathead Shield was used in the construction of the London Underground beginning in 1884. The earth pressure tunnel boring machine, like other TBMs, uses a rotating cutting wheel and an automated soil extraction system. The forward shield is reminiscent of the Greathead design.

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