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The History of the TBM: Towards the Bicentennial
In 2025, we will celebrate the 200th anniversary of the invention of the Tunnel Boring Machine (TBM), a revolutionary technology that transformed the way tunnels are built worldwide. In this column, we will explore the evolution of TBMs, starting from the earliest ideas and prototypes up to the modern machines that now advance beneath rock masses, rivers, and cities with surprising precision and speed.
The Contribution of Schmidt and Kranz
Despite the rapid evolution of TBMs, traditional excavation methods were still preferred over machines in the early 1900s. The moles of the time were bulky, expensive, and above all, they could not adapt to certain geological contexts: essentially, the machines were unable to excavate in rocks characterized by a high degree of hardness. For this reason, interest in mechanized excavation gradually declined during those years.
A significant step in the evolution of TBMs and mechanized excavation was due to the Germans Schmidt and Kranz: between 1916 and 1917, they created the Eiserner Bergmann (literally “Iron Miner”), to facilitate the work of laborers in potash and coal mines, where the rock was softer. This machine featured a drilling head characterized by a large rotating roller equipped with steel tools which, thanks to its size and structure, allowed for the creation of rectangular tunnel sections. Unlike manual excavation, the Eiserner Bergmann was able to operate with greater speed and precision, thus opening up new possibilities in the construction of small tunnels and mining excavations.
In 1931, Schmidt and Kranz introduced a larger and more efficient evolution of the previous model. The new TBM by the two Germans was composed of several elements: a carriage for machine advancement, a support carriage for tunnel stabilization, a cable carriage, and a conveyor belt for removing the excavated material.
The cutting head, featuring a three-arm structure equipped with needles, allowed for an average advance of approximately 5 meters per shift, carried out by a team of five men.
Despite the improvements over the Eiserner Bergmann, this machine still presented some drawbacks: its excessive weight and bulky size made it difficult to maneuver, and a significant amount of time was required to return the machine to the next excavation position.
Nevertheless, this model found important utility, especially for the rapid excavation of ventilation tunnels and exploratory drifts, and it was successfully used in Hungarian lignite mines.
One of the greatest revolutions in the world of mechanized excavation came thanks to the engineer James S. Robbins. In the 1950s, Robbins developed a TBM that forever changed the way tunnels were excavated in rocky environments.
The innovation of his machine consisted of installing a gripper system that firmly anchored the machine to the tunnel walls, thus guaranteeing its stability during the excavation process. This unique feature, combined with the use of rotating disc cutters, allowed for a powerful and effective excavation action. Compared to the previously used carbide versions, these disc cutters showed better durability and superior efficiency, allowing for advancement with speed and stability that were previously unimaginable.
Robbins’ machine found its first application in 1957 for the construction of the Humber River sewage tunnel in Toronto: the combination of grippers and cutters demonstrated its full effectiveness for the first time. During the work, the TBM managed to achieve an advance rate of 30 meters per day, excavating through sandstone, limestone, and clay. Finally, the TBM represented a valid alternative to traditional excavation, proving successful in relatively stable and medium-soft rock types, and marking the beginning of a new era for underground engineering.
The success of the Robbins TBM did not go unnoticed: American companies such as Hughes, Alkirk-Lawrence, Jarva, and Williams joined the race to develop TBMs that exploited the innovative principles introduced by Robbins. It was during this period that machines like the main beam and Kelly types were developed, which remain among the main types used today for major underground works.
Thanks to Robbins, the construction of long tunnels was no longer an insurmountable challenge; his ideas and technical solutions opened the doors to new projects, pushing the use of TBMs well beyond the mining sector. These machines began to be employed in works of great civil and industrial importance, such as the construction of sewage systems, hydroelectric tunnels, and subsequently, road and railway tunnels, becoming an indispensable tool for modern construction.