A tunnel boring machine moves deep slowly through the earth. The entire tunnelling machine is exposed to mechanical loads, dirt, moisture and sometimes high temperatures. A number of harnessed plastic energy chains are used for the energy supply for the segment lining and in material handling. They are exposed to conceivably harsh environmental conditions in a small installation space.
Today's transport infrastructure projects are often based on intelligent tunnel solutions. When drilling goes on below, life above is almost unchanged. This trenchless construction ensures that the traffic, economy and environment are not affected. For example, tunnel boring machines from Herrenknecht AG, Schwanau-Allmannsweier, are always tuned to their respective tasks and geological and hydrological conditions.
As a full-range provider, the company, founded by Martin Herrenknecht in 1977, dominates all geologies and covers the entire range of mechanical tunnel boring technology. It develops, builds and sells mobile tunnel boring machines with diameters from 0.1 to 19 m. These drilled, among other things, the Gotthard Basistunnel, which when completed by 2016/2017 became the longest railway tunnel in the world at 57 km, and have also helped lay pipelines across the continents. The family business includes more than 3,500 employees and 68 subsidiaries and affiliated companies.
In 2010, Herrenknecht was commissioned to build a tunnel boring machine (TBM) in order to build a traffic tunnel in the port of Miami. This was to ease the traffic of almost 16,000 vehicles every day that clog the roads to and from the cruise and freight port in Miami. In particular, many lorries struggle through the inner city. This state is expected to come to an end in 2014 when the "Port of Miami Tunnel" is opened. The traffic will then pass through twin tubes with two lanes each. The port will be more accessible and the flowing traffic can quickly reach the motorway bypassing the city centre.
The pure road tunnel is drilled over a total length of 2,238 metres by a Herrenknecht tunnel boring machine of the earth pressure shield type (EPB = Earth Pressure Balance Shield). The EPB shield has a diameter of 12,860 mm. The drive power of the cutting wheel is 6,300 kW. The whole machine has a weight of 2,500 t; its length is 110 m.
The cutting wheel removes the soil. This passes through the cutting wheel and is conveyed by a screw conveyor onto a conveyor belt and transported away. The tunnel boring machine secures the excavated tunnel through prefabricated concrete segments (so-called tubbings), which form the first lining of the tunnel. The individual tubbing segments are joined together to form a ring using the erector in the rear region of the shield.
The construction time of a TBM of this diameter is around one year. In spring 2011, the tunnel boring machine for Miami began its journey from the production site Schwanau to Miami by lorry and ship. In the third quarter of 2011, it commenced drilling operations. "Every tunnel boring machine is tailor-made to the specific requirements on site," explains Dominik Küntzler, a member of the design staff in the traffic tunnelling department. "These are always pure special designs. On the one hand, space conditions and geology differ on site, on the other hand, equipment details change due to customer-specific requirements. " However, it is the same for all machines that they are almost continuously operating from the day of commissioning to the cut-through.
In the TBMs, which is 110 m long, a number of very different crane systems are used for a wide range of tasks. These are the material handling cranes which transport for example pipes, cable drums and other workshop equipment from the utility vehicles to the respective application site. "These cranes for pipe laying, cable drums and workshop equipment play an extremely important role in the overall process," explains Dietmar Stahl, team leader for crane construction for traffic tunnelling. "They are responsible for the respective supply." For the extension of the conveyor belt, a workshop crane or conveyor material crane is subjected to the heaviest use.
All the above crane systems are equipped with two or three pre-assembled energy supply systems from igus GmbH, Cologne, for longitudinal and transverse travel. On the one hand, the "E4.1" system can be opened at both ends. Energy chains of this series are extremely robust. In addition, their smooth inner surfaces protect the inserted cables, which is proven and tested day by day in this adverse working environment. "We have deliberately opted for the E4.1 series from igus," reports Dominik Küntzler. "On the one hand, the fitters have to mount only one type of chain with this universal chain system." This means that the routine increases and consequently the assembly times decrease. On the other hand, we limit the number of spare parts by relying on this large energy chain modular kit. If a spare part is needed, it must be available very quickly, we cannot afford to have a standstill due to the pressure of time. If the pipe-laying crane does not work, the entire tunnel boring machine does the same. “
Not only in material handling, but also in the erector, which is responsible for placing the tubbing, robust energy supply systems prove their strength. For the tubbing segment lining, immediately after the drilling process, the tunnel is supported permanently with the tubbings in the form of a ring to protect the shield skin. The tubbing segments are positioned on the tunnel wall by means of an erector, a remote manipulator, held mechanically or by vacuum, and then screwed. The concrete sections, which weighs 12 tons per segment, are held by vacuum by the erector at the Miami project. The action radius of the erector of +/- 200° is implemented with energy supply systems of the "E4/4" series with reverse bend radius (RBR) and installed turned 90°.
he chains of the igus E4/4 series are also characterised by high stability and torsional rigidity. They can be opened at both ends and can be equipped with various mounting brackets. Long unsupported applications, also mounted on the side, are implemented just as reliably as gliding applications. The E4/4 plastic chains prove themselves mainly in harsh environmental conditions.
Heavy loads, little space
"Tunnel construction is very tough," says Dominik Küntzler. "The biggest problem is the cramped conditions. Necessary escape routes and pavements restrict the available space more and more. " In this environment the installation size of the energy supply systems plays an important role. These are very compact in the crane systems and allow only small bend radii. With relatively short travels, the material cranes have to mainly transport heavy loads safely to their destinations.
In the already lined tunnels, supply vehicles enter and transport all materials required by the tunnel builders, from the concrete segments down to the tools. This also includes the supply cables for water and sewage. These are taken by the pipe-laying crane from the supply vehicle and automatically mounted on the wall. The individual pipes weigh up to 600 kg. The cables for the power supply are located in a box in a loop, which is pure cable extension. The box is guided from the utility vehicle into the TBM by the cable drum crane. The cables, which weigh up to 8 t, are unwound during the tunnelling, thus ensuring the power supply over the entire length.
Great importance is attached to the conveyor material crane. The conveyor belt transports the waste material to special tailing dumps. During tunnelling, the tunnelling belt must be extended at regular intervals to ensure the further removal of the tailings. The required belt material, which also weighs several tons, is transported in boxes into the tunnel on
the supply vehicles. At the destination, the boxes are set down on the TBM by the conveyor material crane. The tunnel conveyor can then be extended.
Not only the driving machine itself, but also the components in the background have to be designed precisely for the respective requirements on site, so that the tunnelling work takes place within the given time frame. As described above, this applies to a large extent to the energy supply systems of the series E4.1 and E4/4, which have proven themselves in the crane systems and, above all, in the erector, directly behind the drill head, despite the huge dirt accumulation. "Durability and stability play an extremely important role," says Dietmar Stahl. "The energy chains of igus convince us in material and design. We have been working together very successfully for several years. " The Miami Mammoth project also includes the pre-assembly with the most flexible "chainflex" signal and power cables from igus. The supply from a single source with system guarantee is offered by the company under the name "readychain". Dominik Küntzler: "This is how we save a lot of assembly time, among other things. " Even if only a small amount of installation space is available, all cables are protected. The switch cabinet can be installed separately. "This gives us the flexibility we need for this complex task. “