From Wohlmeyer to Grandori: The Evolution of TBMs in Europe

The History of the TBM: Towards the Bicentenary

In 2025, we will celebrate the 200th anniversary of the invention of the Tunnel Boring Machine (TBM), a revolutionary technology that transformed how tunnels are constructed worldwide. In this column, we will explore the evolution of TBMs, from the earliest concepts and prototypes to the modern machines that today advance through rock masses, under rivers, and beneath cities with surprising precision and speed.

From Wohlmeyer to Grandori: The Evolution of TBMs in Europe

Although the first TBM applications took place in Europe, their development on the Old Continent progressed with a slight delay compared to North America. This path was marked by diverse technical approaches, influenced by local geological and infrastructural specificities. European TBMs only truly began to evolve in the 1950s, thanks to a combination of experimentation and the refinement of imported technologies.

The initial European experiments diverged significantly from American models. In Austria, engineer Wohlmeyer developed a technology based on rotating milling wheels, originally intended for lignite mines. Although this technique did not gain large-scale traction, prototypes were successfully used in the Albstollen tunnel in Germany and in some sections of the Seikan tunnel in Japan; however, initial expectations were thwarted in the rocky terrain of the Ruhr.

Another innovation, the Bade TBM—featuring a cutterhead divided into three counter-rotating rings equipped with toothed rollers—proved to be outdated by the time of its testing. Despite these failures, Wohlmeyer’s “undercutting” technology demonstrated significant potential, requiring less thrust force and allowing for the excavation of non-circular sections. This technique was later further developed by companies such as Habegger, Atlas Copco, and Wirth, marking an important phase in the TBM engineering sector.

In the 1960s, German manufacturers like Demag and Wirth began building TBMs inspired by North American models but adapted to European needs. These machines were designed primarily to tackle hard rock, a common requirement for large European infrastructure projects. A fundamental innovation was the adoption of tools derived from deep-drilling technology, such as TCI (Tungsten Carbide Insert) and toothed bits. The introduction of disc cutters with harder coatings significantly improved these machines’ ability to operate in particularly resistant rock, increasing efficiency and reducing maintenance costs.

In the late 1960s, the “reaming” method represented a major innovation. This process involved creating an initial pilot hole, which was then expanded to the desired diameter using a reaming tool. Widely used by Murer, reamer TBMs allowed for the efficient realization of inclined and large-scale sections for the first time, revolutionizing tunnel construction.

During the 1970s and 1980s, focus shifted toward excavation in brittle rock and the widening of sections. In this context, priority was largely given to the concept of ground stability. A significant example was the Mangla Dam project, where a gripper TBM with a diameter of over 11 meters marked a step forward for the adoption of this technology in Europe. However, in the Swiss Heitersberg tunnel, the use of a similar TBM encountered technical difficulties due to the complexity of reinforcement with shotcrete.

A decisive moment arrived with the adaptation of the Heitersberg TBM for the Gubrist tunnel; it was transformed into a shielded machine with precast segmental linings. This approach allowed larger sections to be tackled with greater safety and efficiency. Robbins and Herrenknecht continued the development of these machines, gradually expanding their operating diameters.

Meanwhile, Carlo Grandori, founder of SELI, revolutionized the sector by introducing the Double Shield TBM concept, designed to combine the stability of grippers with the flexibility needed to face heterogeneous ground. Used for the first time in the Sila high-pressure hydroelectric penstock (4.32 meters in diameter), these machines quickly established themselves as a standard for complex projects. In the late 1980s, double shield TBMs demonstrated their full potential during the excavation of the Eurotunnel under the English Channel, operating in chalky and relatively favorable ground. Within a few years, these machines achieved remarkable performance levels, becoming a symbol of what TBM technology could offer.

Bibliography: Maidl B.; Schmid L.; Ritz W.; Herrenknecht M., Hardrock Tunnel Boring Machines, Ernst & Sohn, 2008.