in depth going under

摘要

Earth pressure balance (EPB) tunnelling uses the soil excavated by the drill to create a support structure within the TBM's front shield, unlike other machines that rely on a secondary support medium. The soil is loosened by a cutting wheel and falls through openings into an excavation chamber behind. A pressure bulkhead powered by thrust cylinders controls the soil and forces it into a state of equilibrium where it cannot be further compacted by the ground's earth and water pressure.