Tunnel Boring Machines

The tunnel construction sector covers the building of road and rail tunnels. It also includes the excavation of hydraulic tunnels for hydroelectric projects or to transport effluent. Although tunnel boring machines (TBMs), veritable mobile underground factories, are used to build these structures, it is the spectacular development of metros around the world that has enabled their rapid evolution.

Before the use of tunnel boring machines (TBMs), the mechanization of tunneling operations was limited to the use of point-attack machines derived from mining industry practices, or to the use of drilling machines for projects involving explosives. These techniques are limited to traversing rock massifs. One of the main advantages of TBM technology is that it enables us to cross geological horizons that were previously very complicated and costly to traverse. In fact, the ability to confine the front of a TBM ensures the stability of the excavated face, even in sandy or clayey horizons and below the water table, as well as controlling surface settlement. It is for this reason that the development of new metro lines in urban areas, often located on river plains, has been made economically feasible, and that the TBM industry has seen its activity grow along with it.

The use of TBMs is not confined to metro construction. These machines have also been used to build large-scale bridges. These include the Channel Tunnel, the St. Gotthard and Lötschberg Alpine tunnels, and the Lyon-Turin railway line.

In addition to the fact that the cost of tunnelling using TBMs is lower than that of conventional methods as soon as the length of the tunnels exceeds 2 or 3 kilometers, their use has reduced the number of accidents affecting site personnel.

Although TBM technology is not new, these machines continue to evolve rapidly and constantly. The most recent developments are aimed at broadening the range of terrain that can be excavated by a given type of TBM, detecting potential obstacles, or increasing digging performance.