pressure-on-the-face mole

tunnel machine

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July 13, 2026

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A "pressure-on-face mole" is a type of tunneling machine that excavates tunnels by applying pressure directly to the face of the excavation. This method allows the main tunnel to operate in free air, reducing labor costs associated with working under pressure. These machines are designed to excavate earth with drag teeth and move the excavated material onto a conveyor belt, often operating within a protective shield. The pressure-on-face technique has been used in various soil types, including sands, silts, and volcanic clays, with the slurry of excavated material sometimes removed by pipeline. This technology aims to make tunneling more efficient and cost-effective.1

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tunnels and underground excavations
Soft-ground moles
A third type is the pressure-on-face mole. Here, only the face is pressurized, and the tunnel proper operates in free air—thus avoiding the high costs of labour under pressure. In 1969 a first major attempt used air pressure on the face of a mole operating in sands and silts for…
Read More
A third type is the pressure-on-face mole. Here, only the face is pressurized, and the tunnel proper operates in free air—thus avoiding the high costs of labour under pressure. In 1969 a first major attempt used air pressure on the face of a mole operating in sands and silts for…
Read More