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The tunnel boring machine is around 120 metres long, seven metres high and is also affectionately known as the ‘mole’, it bores slowly through the soil, carrying all the necessary equipment along with it.

The most important section is the drill head.

It consists of drill heads that cut through soil and stone. Behind this, auxiliary equipment can be found for removing the excavated material, as well as for securing and enlarging the tunnel.

The two tunnels for the U2 lines between the Matzleinsdorfer Platz and Lerchefelder Straße are being built using this method.


Mode of operation of the tunnel boring machine

Rotating scraper blades and cutting rollers loosen the soil from the in-situ face.

A screw conveyor transports the excavated material onto a conveyor belt, while hydraulic cylinders continuously press the machine forward.

The tunnel tube is lined with prefabricated reinforced concrete segments known as segments.

Shotcrete nozzle

The nozzle is used to apply concrete to the tunnel wall, which is lined with steel grids.

The concrete supplied in a thick hose is mixed with water shortly before it emerges.

Due to its special composition, the shotcrete hardens almost immediately after hitting the wall.

Total station

For tunnel construction, the alignment of the already completed tunnel tube with its target direction is of crucial importance.

An important measuring instrument for this is the theodolite.

It can be used to measure horizontal and vertical angles precisely.

A total station is a special type of theodolite and is equipped with a distance meter.


Parts of the tunnel boring machine

Tunnelbohrmaschine

Tunnel boring machine driving up
Von Ingbife – Eigenes Werk, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=29742705

Drive motors

Depending on the diameter of the tunnel boring machine and the geological requirements, more or less hydraulic or electric motors turn the cutting wheel.

Drill head

The most important part is the drilling head.

With the cutting wheel, the machine bores into the ground.

Immediately behind it, the so-called erector joins the tunnel segments (segments) to form a tunnel tube.

Erector

The individual tunnel segments (segments) are transported to the erector in a precisely specified sequence. The erector lifts them with a suction plate, swivels them to the appropriate position on the tunnel wall and places them with millimeter precision against the segments already inserted.

The erector is usually controlled by a mobile control module.

Screw conveyor

The screw conveyor transports the excavated material from the excavation chamber to the back-up conveyor. In the case of earth pressure shields, it also ensures that a counterpressure is maintained directly behind the cutter wheel: only enough soil material is removed from the excavation chamber via the rotational speed of the auger to ensure that the counterpressure remains stable.

Supply rail tracks

The rail tracks are used to transport material and personnel from the tunnel opening to the tunnel boring machine.

Hoisting system

Here, the tunnel segments (segments) are taken from the supply and lifted onto the conveyor system of the tunnel boring machine.

Muckring

Conveyor hopper that transfers the mined material from the screw conveyor to the conveyor belt.

Trailing conveyor

The downstream conveyor, i.e. the part behind the boring head, is responsible for transporting the segments (tunnel components) and for removing the demolition material.

The downstream conveyor transports the demolition material to the end of the tunnel boring machine. From the trailing conveyor to the tunnel exit, material wagons (freight cars) on rails or a conveyor belt take over these tasks.

Personnel airlock

The personnel airlock provides access to the front area of the tunnel boring machine (TBM) for tool changes or maintenance work.

If the TBM is of the hydroshield type, a counterpressure is built up behind the cutting wheel to the earth and groundwater pressure present in order to prevent uncontrolled penetration of the ground material.

For this reason, the personnel lock in this type is designed as a pressure chamber, and serves to acclimatize to the pressure difference, as in a dive.

Peeling knife

Peeler blades are mining tools used mainly in softer, silty or clayey soils, such as the Vienna soil.

Shield casing

The shield casing protects the working area of the tunnel boring machine from external earth and groundwater pressure. In the rear area, the completed tunnel segments take over this task.

Cutting roller

Cutting rollers are made of special hardened steel and weigh about 200 kilograms. The number of cutting rollers on a cutting wheel depends on the soil conditions: The harder and rockier the ground, the more cutting rollers are used.

Control station

The tunnel boring machine is operated from the control stand.

The control station is the “control center” of the tunnel boring machine. All parameters relevant for driving are collected and monitored here. These include driving speed, navigation and pressure conditions.

Segment

Segments are made of reinforced concrete and, when assembled, form a tunnel ring. Segments are designed in such a way that a standard shape can be used for both straight tunnel sections.

For this purpose, they have beveled side surfaces. If they are joined in the same direction, a curve is formed. When installed on straight sections, they are installed alternately in opposite directions.

Supply unit

It contains, among other things, power supply units and containers for construction materials and compressed air.

Jacking presses

Hydraulic cylinders press the tunnel boring machine forward from the last tunnel ring built.

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