Earth pressure balance, or EPB, is a mechanised

tunnel A tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent tunnels have used immersed tube cons ...

ing method in which the excavated material is used to support the tunnel face whilst it is being plasticised using foams/slurry & other additives to make it transportable and impermeable. The

spoil Spoil or spoils: *Plunder taken from an enemy or victim *Material (such as rock, earth or other overburden) removed during: **excavation **mining **dredging Dredging is the excavation of material from a water environment. Possible reasons f ...

is admitted into the

tunnel boring machine A tunnel boring machine (TBM), also known as a "mole", is a machine used to excavate tunnels with a circular cross section through a variety of soil and rock strata. They may also be used for microtunneling. They can be designed to bore throu ...

(TBM) via a

screw conveyor A screw conveyor or auger conveyor is a mechanism that uses a rotating helical screw blade, called a "''flighting''", usually within a tube, to move liquid or granular materials. They are used in many bulk handling industries. Screw conveyor ...

(cochlea) arrangement which allows the pressure at the face of the TBM to remain balanced without the use of slurry. This has allowed soft, wet, or unstable ground to be tunneled with a speed and safety not previously possible. The

Channel Tunnel The Channel Tunnel (french: Tunnel sous la Manche), also known as the Chunnel, is a railway tunnel that connects Folkestone (Kent, England, UK) with Coquelles ( Hauts-de-France, France) beneath the English Channel at the Strait of Dover. ...

, the

Thames Water Ring Main The Thames Water Ring Main (TWRM, formerly the London Water Ring Main) is a system of approximately of concrete tunnels which transfer drinking water from water treatment works in the Thames and River Lea catchments for distribution within c ...

, sections of the

London Underground The London Underground (also known simply as the Underground or by its nickname the Tube) is a rapid transit system serving Greater London and some parts of the adjacent ceremonial counties of England, counties of Buckinghamshire, Essex and He ...

, and most new

metro Metro, short for metropolitan, may refer to: Geography * Metro (city), a city in Indonesia * A metropolitan area, the populated region including and surrounding an urban center Public transport * Rapid transit, a passenger railway in an urba ...

tunnels completed in the last 20 years worldwide were excavated using this method. EPB has historically "competed" with the

slurry balance A slurry is a mixture of denser solids suspended in liquid, usually water. The most common use of slurry is as a means of transporting solids or separating minerals, the liquid being a carrier that is pumped on a device such as a centrifugal pu ...

method of mechanised tunneling where the slurry is used to stabilise the tunnel face and transport spoil to the surface.

See also