Tunnel Information

Earth pressure balance tunnel boring machine (EPB TBM)
Earth pressure balance tunnel boring machines
Historically, EPBs were developed in order to do away with the mucking system and the reprocessing of boring slurry. To do this, the soil must ideally consist of fine elements (clay and silt) and natural water. This type of mix is rare, which is why foams were developed.

Basic principle
The earth pressure balance tunnel boring machine or EPB consists of a cutting chamber located behind the cutterhead. This chamber is used to mix the soil + water foam. It is maintained under pressure by the mucking system. The system consists of a screw conveyor whose speed is controlled so that constant pressure inside the chamber is guaranteed. The material exits the screw conveyor via a hatch that can be closed when the TBM is shut down. The material is then removed by a belt conveyor and/or train cars circulating in the tunnel.

Double shield tunnel boring machine (TBM)
This type of boring machine is used for tunneling in stable to unstable rock for the excavation of traffic tunnels (road and rail), supply tunnels (water, gas and electricity) and other special applications.
The main elements in the construction of the shield tunnel boring machine are the shield which gives the machine its name, a construction like a steel tube in which all other components of the machine are embedded, the cutter head and its drive housing, the advance mechanism and the robot-like device for installation of the tunnel lining, the so-called erector. The tunnel lining, usually consisting of prefabricated concrete sections, is installed with the erector, protected by the rear shield mantle, the so-called tail shield.

Gripper tunnel boring machine (TBM)
This type of boring machine is suitable for driving in stable rock and is used for the excavation of traffic tunnels (road and rail), supply tunnels (water, gas and electricity), pressure water utility tunnels for hydroelectric plants, tunnels for cable cars high in the mountains, tunnels for geological investigations and other special applications.
The main elements in the construction of the open tunnel boring machine are the cutter head with its associated drivehousing, the support construction (the so-called gripper) and the advance mechanism.

Mixshield tunnel boring machine (TBM)
Tunneling systems for mixed ground
Dual mode - two process technologies in one
As the term 'dual mode' indicates, two process technologies are combined in these machines.
Shield machines
These machines are externally similar to shield machines and combine the functional features of a hard-rock shield tunnel boring machine and, optionally, of a slurry shield or a hydroshield machine (Bentonair, slurry shield). They are always used when tunnels have to be driven alternately in stable and unstable sections.
New style machines
Dual-mode tunnel boring machines are still a new type of machines and have been developed to meet the requirements of complex projects in strongly varying geologies. Where conventional tunneling techniques had to be used formerly, these machines now open the way to lower-risk and lower-cost tunneling in difficult geological conditions

Slurry pressure balance tunnel boring machine (SPB TBM)
Slurry shield tunnel boring machines
Bentonite slurry, consisting of a specific clay and water mixture is universally used in boring and digging operations. The slurry has numerous properties: sealing of the cutting face, reduced friction on the TBM's structure, and transport of cuttings to the separation plant outside the tunnel.
The basic principle of this TBM is to maintain the tunnel's cutting face during the excavation phase by filling the working chamber, located behind the cutterhead, with slurry.
Slurry pressure is carefully controlled by a large air bubble which is maintained by a separately-controlled air supply system. This air bubble acts as a damper by absorbing sudden variations in mucking output.