This is a general guide for how much a Tunnel Boring Machine (TBM) would cost. It is not realistic to give exact figures in ever changing marketplace, though certain factors effecting TBM prices generally remain constant. Therefore it is better to mention the factors effecting the price of a TBM.

Remember that, when you want to buy a TBM, you don't have any showrooms of TBM Manufacturers to visit. Almost all the time, TBMs are custom built, after they are ordered. 

The cost of a tunnel boring machine (TBM) basically depends on following parameters:

• TBM Diameter

The boring diameter of a TBM is an important factor in determining its price. As a general rule (with occasional exceptions), one can assume that as the diameter increases, so does the price tag. But the this increase is not really linear.

It is just a matter of economics. Certain TBM diameters (e.g. so-called "subway size" of around 6 meters of diameter) are high in demand. Therefore they are produced by more manufactures in greater numbers. Hence in turn, their spare parts, like the main bearings of this size are available often off-the-shelf and at competitive pricing. As a typical TBM consists of around 10-15 thousand parts, economies of scale also works here. For that reason, a "subway size" TBM may occasionally cost less than a smaller but custom-size TBM.

For that reason, the price increase from the "subway size" to say, 7 meters will not be a linear increase.

An often quoted general rule of thumb for the price of a Tunnel Boring Machine is US$ 1 million for per meter in diameter. Thus, a TBM of 8 meter in diameter would cost around US$ 8 millions. In reality, the increase in price is not so linear as the diameter increases. For smaller-diameter TBMs, you will often see that the increase in price will be lower than a million dollars per meter. And as the diameter increases, especially from "subway size" to bigger diameters, the price differential will be more than a million dollars. Especially for the large diameter TBMs used for multi-level, multi-track, multi-lane tunnels, the price per meter will be much higher, as such an increase in diameter comes with some exponential increase in complexity. It is not just bigger sizes from the point of TBM design.

Prices of TBMs have come down rather radically in recent years largely thanks to the Chinese TBM manufacturers. Before China's TBM manufacturers flooded the market with World-class TBMs, the cost was around US$ 1,5 million per meter in diameter. Nowadays with some Chinese TBMs for "subway size" this can be as low as US$ 700-500 thousands/meter.

• TBM Type

Tunnel Boring Machines are produced for various geological conditions and their complexity varies accordingly. As expected, the more complex a TBM is, the more expensive it will be. For example the cost of a single shield mixed ground TBM that you use in uninhabited areas is usually the lowest. On the other hand, if you need to bore a tunnel under a sprawling city center, you'd better use an Earth Pressure Balance (TBM) which will be more expensive. For certain geological conditions, there will be a need to use Slurry TBMs which generally tend to be even more expensive.

• TBM Manufacturer

Like everything else, there are buyers who are prepared to pay extra for a certain brand. This may be due to some perceived level of quality for a familiar TBM brand which has been around for decades. People are understandably timid in trying out a new brand even if it offers a better price/performance ratio. And this allows the established brands to charge extra for their products and service.

Of course, there will be many cases when a certain brand will be offering a better quality at a higher price. You pay what you get for.

• Project Prestige, Market Considerations

Sometimes TBM manufacturers go to great lengths to supply TBMs to a prestigious project. An important project will be a showcase for them, free publicity for established brands and a validation tool for the new coming brands. TBM manufacturers can come up with great price/performance packages to get their TBMs selected. In other cases, it may be a priority for a brand to get a foothold in a certain market. For example, a manufacturer which has never delivered a TBM in a west European country, may be willing to make an attractive offer.