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Herrenknecht - Model Mixshield -Tunnelling Machine
The Mixshield technology developed by Herrenknecht is a further development of conventional slurry support technology. The support pressure is precisely adjusted using an automatically controlled air cushion. This means that heterogeneous geologies and high water pressures of up to more than 15 bar can also be safely managed, even with very large excavation diameters.
Greater safety thanks to precise support pressure control
In Mixshield tunnelling, a largely impermeable membrane is created at the interface between the ground and the bentonite suspension. It is only this that enables the required support pressure to be built up while at the same time it seals the tunnel face against groundwater. For exact and precise support pressure control at the tunnel face, a bulkhead separates the slurry-filled chamber into a front excavation chamber and a rear intermediate chamber, the working chamber. In the intermediate chamber, the support pressure is generated by a pressurized air bubble and transferred to the bentonite suspension. Communication between the two chambers takes place via a bulkhead opening in the invert area.
Sealing against high water pressures
Thanks to the closed, hydraulic slurry circuit, Mixshields can be used safely even at high water pressures of over 15 bar. The prerequisite is an appropriate seal between the atmospheric part of the machine and the ground ahead of it. This is why Mixshields are equipped with a multiple seal system. The drive is designed as a system with individual sealing chambers with a pressurized sealing compound. At the end of the machine, the annular gap between the atmospheric tunnel and the outside of the segments is protected against water and soil ingress by several rows of steel brushes and by filling the gaps with sealing compound.
- Maximum tunnelling safety thanks to precise tunnel face support with continuously regulated pressurized air cushion in the working chamber
- Can be used at high water pressures of over 15 bar
- Even the largest diameters up to 19 meters can be realized
- Various special solutions available for special project requirements
- Geology: Heterogeneous ground Sandy and gravelly soils, heterogeneous ground with high water permeability and pressures (sand, gravel, consolidated rock)
- Diameter: 4 - 19 m
Safe preparation for conveying
Mixshield drives in non-cohesive, heterogeneous soils often involve larger rocks or blocks of stone. Such boulders are crushed down to a conveyable size for smooth hydraulic removal. With Mixshields, a claw crusher placed in front of the grid is often used to crush the stones to a conveyable size. If fine-grained, cohesive soils are to be expected along the alignment, a roll crusher in front of the intake is used as an alternative. With the help of the laterally arranged mixing blades, the roll crusher conveys the material into the intake and crushes larger clods of clay.