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Tunnel Boring Machines
8:46 A tunnel borer building its own concrete lining behind it. Filmed and published by Herrenknecht AG. Plays from YouTube, nothing here is re-hosted.
What it does
A tunnel boring machine digs a tunnel and builds it at the same time. It is not a drill. It is a mobile factory a couple of hundred meters long that eats ground at the front, processes the spoil down its length, erects a finished concrete tunnel lining behind itself, and pushes off that lining to move forward.
How it works
A rotating cutterhead studded with disc cutters or cutting teeth presses against the face. In soft, wet, urban ground an earth pressure balance machine keeps the excavated soil itself pressurized in a chamber behind the cutterhead, so the pressure in that chamber balances the groundwater and earth pressure outside and the street above does not settle. A screw conveyor meters the spoil out of that chamber, and the discharge rate of that screw is how the operator controls face pressure. Hard rock machines do the opposite: they grip the tunnel walls with hydraulic pads and shove the cutterhead into solid stone, where the discs crush the rock into chips rather than cutting it. Behind the shield, an erector arm swings precast concrete segments into a ring and bolts them together. The thrust rams then push against that completed ring to advance, and the cycle repeats.
The numbers
Earth pressure balance machines are built in diameters from roughly 3.5 meters up to about 17.6 meters, which is the largest diameter we can confirm has actually been delivered and driven. Larger diameters appear in manufacturer proposals rather than in finished tunnels. A mid-size metro machine at around 6.8 meters diameter runs roughly 120 meters long and weighs about 1,100 tonnes complete with backup gantries. Cutterheads are transported as single pieces on multi-axle trailers and become minor news events when they move.
Who uses one
Metro authorities, water and sewer utilities, road and rail projects, hydroelectric schemes and mining shaft contractors. Machines are frequently specified for one project, built to that geology, and then refurbished for the next.
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8:51 Giant MachinesHow a hard rock tunnel boring machine cuts stone
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Looking for one of these?
APE does not trade tunnel boring machines. What we do trade is the plant that works around one: cranes, compressors, generators, pumps, conveyors, segment handling and shop equipment. Tell us what the job needs.
American Plant & Equipment has been buying and selling industrial machinery out of Roebuck, South Carolina since 1975, with 97,000 machines in inventory. Tell us the process you need to run and we will go and find the machine, or we will move the one you are finished with.
Prefer to talk? Call (864) 574-0404 or email sales@americanplantandequipment.com.