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Almost every ground can be mastered safely by Herrenknecht AVN machines.
AVN machines in operation
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.
Cutter heads for soft soils, mixed soils, and rock: Herrenknecht offers the right solution for every geological challenge.
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.
In cohesive soils, various sprinkler systems successfully prevent clogging in the excavation chamber.
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.
Operating principle at a glance:
Cutting knives and disc cutters remove the soil.
Hydraulic support using slurry suspension.
Hydraulic conveying of the muck via a closed slurry circuit.
Depending on the selected method (pipeline or tunnelling), this is carried out with a thrust unit, e.g. a jacking frame in the launch shaft or hydraulic thrust cylinders in the shield.
Pipe jacking, Direct Pipe®, E-Power Pipe® or segmental lining.
Precisely around curves
Depending on project requirements, various navigation solutions are available for controlling AVN machines, depending on the selected lining method. You can find more information on this in the Navigation and Monitoring section.
With AVN machines, an additional door behind the cutterhead allows access to the tunnel face.
Access to the tunnel face
Accessible AVN machines can be equipped with a door to allow access to the tunnel face. This may be necessary to remove obstacles or to change the cutting tools. The cutting tools are mounted in such a way that they can be changed from the rear. Changing tools allows longer drive lengths, especially in hard rock. If necessary, personnel can be safely brought into the pressurized area via a personnel airlock.
Tunnelling without reception shaft
So-called blind-hole tunnels are a special challenge, especially in non-accessible microtunnelling diameters. Blind-hole tunnels end directly in the ground, making conventional recovery of the machine impossible. Herrenknecht has developed special cutterheads with a fold-away mechanism for this very special application. When the required drive length has been reached, the microtunnelling machine can be pulled back to the launch shaft with its cutterhead folded away. The jacking pipes remain in the soil. A typical project application of blind-hole tunnels is for pipe arches. Steel pipes are installed side by side in the ground to form a pipe arch. Protected by this arch, the actual tunnel diameter is then excavated using mining techniques. Crossings beneath railway lines can be excavated and metro stations can be built safely. A further application of blind-hole tunnels is the installation of house connections or tunnelling operations in which the reception shaft has not yet been completed for logistical reasons.
With AVND machines, the additional air cushion for support pressure regulation reduces pressure peaks in the excavation chamber.
AVND with compressed air support for maximum safety
For additional safety in inhomogeneous, less stable geologies and with larger diameters, the AVN technology has been enhanced with compressed air support (AVND). AVND machines have a two-part excavation chamber. Compared to Mixshields, the support pressure is controlled via a communicating tube and an automatically regulated air cushion in the pressure chamber. This enables even more precise control of a heterogeneous tunnel face and smooths out pressure peaks in the excavation chamber. AVND machines are therefore specialists for settlement-sensitive tunnelling, even under high groundwater pressure and with low overburden.
AVNS with jet pump for long distances with small diameters
The AVNS machine is a further development of the AVN series to realize longer drives in small, non-accessible diameter ranges. A jet pump as a slurry pump and a hydraulic unit were integrated into the AVNS machine concept. The AVNS350XB (Ø 505 mm) is the centerpiece of the E-Power Pipe® method.
The all-rounders
Thanks to their wide range of applications, AVN machines from Herrenknecht have already proven themselves successfully in hundreds of projects worldwide. With the sophisticated machine technology, even the most difficult tunnelling sections in pipe jacking or segmental lining are driven safely, quickly and efficiently.
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Steffen Dubé
President and General Manager Herrenknecht Tunnelling Systems USA Inc.
Gerhard Goisser
Commercial Manager Herrenknecht Tunnelling Systems USA, Inc.