Herrenknecht’s method of installing cable protection pipes gets shortlisted for bauma Innovation Award
Herrenknecht has developed a new method to quickly and securely install small-diameter cable protection pipes underground with drive lengths of more than one kilometre.
Dubbed E-Power Pipe, Herrenknecht says the trenchless method of installing underground cables is more environmentally and financially friendly than the traditional open-cut process for high-voltage grid expansion.
E-Power Pipe combines the proven horizontal directional drilling (HDD) and AVN or Direct Pipe drilling technologies. The centrepiece is the newly developed AVNS350XB tunnel boring machine, developed by Herrenknecht, with an excavation diameter of 505 mm.
The new development from Herrenknecht is one of three finalists for the bauma Innovation Award 2019 in the Machine category, alongside the new large Milling machine with Mill Assist from Wirtgen and the 370 EC-B fiber flat-top crane from Liebherr.
Trenchless tech
Trenchless technology offers significant advantages over the conventional open-cut method, according to Herrenknecht. The procedure closes a technical gap as it allows small diameter drives with 10 times greater lengths, shallower depths as well as high precision and speed.
With E-Power Pipe, underground cables can be installed trenchlessly and close to the surface at depths of between two and four metres with minimal intervention in the landscape.
The heart of the system is the remote-controlled tunnel boring machine (TBM) AVNS350XB. The machine can keep to the planned alignment with high precision and cross safely under existing infrastructure such as pipelines, roads, railways or small bodies of water. Individual boreholes can be placed a distance apart of one to two metres, so several lines can be installed in parallel.
The tunnelling machine is equipped with a jet pump and an integrated hydraulic power unit.
With conventional methods, space restrictions limited muck removal over longer sections, and as a result also limited the possible drive lengths. Through the use of the jet pump for transporting the muck, up to 10 times longer tunnelling distances can be achieved at high speeds in the small diameter range.
Two-stage installation
At the starting point, a newly-developed push and pull unit is installed and its thrust is used to push the jacking pipes and the TBM along the specified route in the direction of the target point. The borehole remains securely supported by the machine and the jacking pipes throughout the process.
After breakthrough at the target point, the TBM is separated from the jacking pipes. Next, the prefabricated cable protection pipe is connected to the jacking pipes, which are still located in the borehole, and pulled back and into the borehole by the push and pull unit in the launch shaft at the other end.
After installation of the protection pipe, the E-Power Pipe mission is complete.
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Final insertion of the underground cables is carried out by specialized companies.
The method involved the development of new, extended jacking pipes that allow a much more continuous advance.
Herrenknecht developed an appropriate push and pull unit with a 10-metre stroke and a push and pull force of 350 tonnes specifically for the jacking pipes.
As well, by rotating it 180 degrees in the launch shaft, it can also handle the retraction of the cable protection pipe and take on a second function.
The technology is based on a rack and pinion guide, powered by electric motors.
As a result, the innovative concept ensures higher installation performance and greater acceptance thanks to lower noise emissions.
Pilot project
The E-Power Pipe was successfully demonstrated in a pilot project in West Germany.
Three parallel holes with a length of 300 metres at a shallow depth were bored for the installation of HDPE pipes for future cable insertion.
Daily best performances were achieved of 184 metres during tunnelling and 266 metres when pulling in the protective pipe.
The development of the method received funding from Germany’s Ministry of Economics and Energy, and was carried out by Herrenknecht in cooperation with Amprion GmbH and with RWTH Aachen.
Small footprint
Due to the trenchless installation method, earth movements are reduced at the places where cables will eventually be connected. This equals a reduction of about 90 per cent in relation to the entire alignment.
Installation takes place without any environmental impact over long distances, since the surfaces and the soil structure are left largely untouched. The use of construction machinery and trucks is also significantly reduced, alongside noise and emissions.
The required personnel and associated costs are also lower compared to open-cut installation. With the same number of personnel, several sections of line can be worked on simultaneously.
bauma award
The bauma Innovation Awards will be announced in mid-April in five categories. A panel of experts evaluates the practical relevance, economic potential and contribution to environmental protection of the innovations.
