The demand for efficient new infrastructure systems is increasing and automatically leads to the underground as living space above ground is becoming more and more scarce. This also applies to the mechanical construction of tunnels, which is almost completely carried out in underground thanks to the tailor made tunnelling technology made by Herrenknecht. Mechanized tunnel excavation has entered new dimensions in terms of size, length, geological complexity and depth of underground constructions. It sets the standards regarding safety, profitability and environmental protection – in Traffic Tunnelling projects as well as in the trenchless construction of Utility Tunnels, such as sewer, water, cable tunnels and oil and gas pipelines. Different machine types and working principles have been developed to master the geological and hydrological requirements of tunnelling projects worldwide. This paper gives an overview on state-of-the-art hard rock tunnelling equipment and project possibilities but will also highlight the innovative and current design approaches to overcome the difficult specific project conditions of hard rock projects of today. Reference projects and experiences world wide show the feasibility of tunnel visions and the infrastructure importance for the respective area.


The tunnel projects that are realized today face more and more complex conditions. This because of the increasing need for infrastructure systems in rough terrain or in municipal areas where space above ground is limited. The project challenges in hard rock are generally high overburden, long tunnel drives, strong and abrasive rocks as currently faced with the construction of the longest railway tunnel, the Gotthard Base Tunnel in Switzerland.

These complex projects demand for a safe and economical tunnelling technology, both in hard, solid rock conditions and in soft rock, which is provided by mechanized tunnelling.

The cited projects focus on representative tunnelling jobs where mechanized tunnelling technology was applied.


Dependent on the rock quality different types of hard rock machines are available on the market. In general Gripper TBMs are applied to solid rock conditions whereby Shielded TBMs such as Single Shields and Double Shields, are generally used in soft rock or unstable hard rock conditions. Apart from the drilling technology, efficient and economical material transport from the tunnel face to the end of the tunnel is also a key requirement for a successful excavation process.

2.1 Gripper TBM

This type of hard rock machine is typically applied to stable and massive rock conditions with low water ingress. The cutterhead is of flat face design and equipped with disc cutters to suit the rock conditions. The cuttings will be removed from the tunnel face via buckets. They are arranged at the circumference of the cutterhead and are supported by additional backscrapers on the rear side of the cutterhead.

A conveyor belt along the TBM is used for the removal of excavated material from the excavation chamber to the discharge point of the material transport system in the tunnel.

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