The Variable Density TBM

Technological advances in mechanized tunnelling are constantly pushing back the limits of what is possible. Herrenknecht developed the Variable Density TBM to enable safe tunnelling in heterogeneous, variable and highly permeable soft geologies. The machine’s design has proven itself over the past ten years, successfully coping with highly complex project parameters – and several current projects are showing that it has even greater potential.

Technology and references

Metro Lyon

Mastering Extremes

A Herrenknecht Variable Density Tunnel Boring Machine (TBM), operated by experienced miners at Implenia France, excavated a metro tunnel through some extremely challenging geology in Lyon. There was no need for the costly and time-consuming process of stabilizing the ground – heterogeneous, highly permeable ground, with a layer of granite in the alignment − before work could begin. A superior technology for mechanized tunnelling in highly complex heterogeneous geology.



Variable Density TBM technology offers a number of advantages. Depending on the circumstances in each specific project, the technology can help to protect the environment, reduce the overall budget or enhance the jobsite logistics.

“It is now common knowledge that Variable Density TBMs make it possible to tunnel through many different types of ground. However, they also allow you to process the excavated material in the separation plant so that some of it can be reused. As awareness of the need to reduce our impact on the planet grows, this will soon be a key factor in people’s choice of TBM type.”

François Renault,
Tunnel Technical Director, Vinci Construction Grand Projets, Hampton Roads Bridge
Tunnel Expansion

“The major geological challenge the project posed was the need to avoid settlement. The final
outcome was very good indeed.”

Denis Vialle,
Technical Director, Implenia France, Lyon Metro Line B

Your contact

Tunnelling in complex softground?

We are ready!

Frédéric Battistoni

Frédéric Battistoni

Head of Project Management
Business Unit Traffic Tunnelling

Matthias Schwärzel

Matthias Schwärzel

Division Manager Project Management
Business Unit Traffic Tunnelling