With E-Power Pipe, Herrenknecht has developed a new method to quickly and securely install small-diameter cable protection pipes underground over long distances of more than 1 km. The company said this system has purposefully modified and further developed proven drilling technologies so that in the future, underground cables can be installed trenchlessly and close to the surface at a depth of between 2 m and 4 m with minimal intervention in the landscape.
At the heart of the system is the AVNS350XB, a fully remote-controlled tunnel boring machine (TBM) with an excavation diameter of 505 mm and is designed for drive lengths of more than 1,000 m. The machine can keep to the planned alignment with high precision and thus cross safely under existing infrastructure such as pipelines, roads, railways or smaller bodies of water. Individual boreholes can be placed a small distance apart of only 1 – 2 m, 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 drive lengths possible, said Herrenknecht. 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.
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 the whole time. After breakthrough at the target point, the TBM is separated from the jacking pipes. Subsequently, the prefabricated cable protection pipe is connected to the jacking pipes still located in the borehole and pulled back and thus 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. Final insertion of the underground cables is carried out by appropriately specialised companies.
The method innovation involved the development of new, extended jacking pipes that allow a much more continuous advance. Herrenknecht also developed a push and pull unit with a 10 m stroke and a push and pull force of 350 t specifically for these jacking pipes. 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.
According to Herrenknecht, E-Power Pipe has already been successfully demonstrated in pilot projects. Daily best performances were achieved of 184 m during tunnelling and 266 m when the protective pipe was pulled in. The development of the method received funding from the Federal Ministry of Economics and Energy (BMWi research project IBoTec) and was carried out by Herrenknecht in cooperation with Amprion GmbH and RWTH Aachen.
The installation of underground cables using E-Power Pipe is a ground-conserving alternative to the conventional open-cut method. Due to the trenchless installation method, earth movements are reduced at the places where HVDC cables have to be connected later. This can mean a reduction of about 90% in relation to the entire alignment, revealed Herrenknecht. 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 in this way, as are noise and emissions.
E-Power Pipe is a winner of the bauma Innovation Award 2019 in the ‘Machine’ category.