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Herrenknecht - Model AVN -Tunnelling Machine
Herrenknecht AVN machines (AVN is short for the German for Automatic Tunnelling Machine Wet) are slurry pressure shields, also known as slurry machines. Equipped with a cone crusher, AVN machines really come into their own in non-accessible tunnel diameters and ensure safe tunnelling. The slurry support of the tunnel face enables AVN machines to be used in all types of ground: from silt and clay to non-cohesive soils and gravel through to rock, both in pipe jacking and segmental lining.
- Geology: Soft ground Heterogeneous ground Rock
- Diameter: 0.4–4.8m
Cutting wheel design according to ground conditions
The soil ahead is removed by full-face excavation using a cutting wheel specially tailored to the expected ground conditions. Standard or mixed soil cutterheads are used in soft soils and mixed geologies. A rock cutterhead with disc cutters is installed for drives in stable rock. Parallel to the advance, a tapered cone crusher in the excavation chamber crushes stones or other obstacles to conveyable grain sizes. The material then falls through sieve-like openings in front of the intake and is sucked out with the suspension via the slurry line.
Expandable diameter
The excavation diameter can be flexibly enlarged within a certain range using an extension kit and an adapted cutting wheel. This means that in pipe jacking in particular, with an AVN machine, different diameters can be realized and different pipe materials can be used.
All advantages at a glance:
- Can be used in almost all ground conditions
- Can also be used with high water pressures
- Maximum tunnelling safety thanks to hydraulic face support
- Precise control even with vertical and horizontal curves
- Ideal technology for tunnelling in non-accessible areas (microtunnelling)
- Very long pipe jacking distances over 1,000 m possible thanks to intermediate jacking stations
Sprinkling for smooth material transport and high advance rates
Especially in cohesive soils, it can be difficult to keep the cutting wheel and crusher zone free of clogging. Based on years of project experience, Herrenknecht has developed suitable sprinkler systems for different types of ground. High-pressure nozzles in the cone crusher inject additional water for cleaning, which cuts up the loam or clay and prevents clogging in the crusher zone. Medium-pressure sprinkling takes place via the bentonite injectors. Changing the nozzle cross-section allows the suspension pressure to be adjusted, thus optimizing the material flow.
An optional camera system in the excavation chamber provides the machine operator with additional visual wear and situation monitoring (from AVN 1200).
Pipe jacking over great distances
AVN Machines are often used in pipe jacking operations. The maximum drive length depends on several factors such as skin friction, available jacking force, or the nominal diameter of the jacking pipes. Automatic lubrication systems reduce the friction between pipe skin and soil by injecting bentonite into the annular gap. In the range of diameters that allow man-entry it is possible to use additional hydraulic intermediate jacking stations. These are installed in the pipe string at intervals which are defined specifically for each project. By dividing the pipe string into individual sections, the necessary thrust force is reduced and distributed respectively. This means that the distance between launch and reception shaft can be more than 1,000 meters, depending on the project conditions and the number of intermediate jacking stations.