New installation method for electricity pipes: A debut for KaRoSch, an innovative laying carriage made by Bohlen & Doyen
For the underground cabling section of grid operator Tennet’s Wahle Mecklar pilot project, Bohlen & Doyen GmbH used its novel cable-and pipe-laying carriage named “KaRoSch”. This innovative laying technology for electricity pipes can greatly boost efficiency by making installation up to 25 % faster, improving occupational safety and achieving a marked reduction in resource consumption.
The energy transition requires new power lines. In regard of this situation, the focus is on the grid in the heart of Germany by extending power lines running right across it from the North to the South. The just under 230 km connection runs from the substation in Wahle, between Peine and Braunschweig, to the Mecklar substation in near Bad Hersfeld in Hessen. What makes this project special is the fact that Wahle-Mecklar is one of four alternating current pilot projects which are legally permitted to use underground cabling for some pre-defined sections. Geographically, the sixth construction lot of section C is located between Hetjershausen and Olenhusen close to Göttingen. This is where, over a length of approx. 5.5 km, one of the two underground cabling sections of the Wahle-Mecklar power line are being constructed, Bohlen & Doyen used their new KaRoSch for the Götting section.
Building transmission grids often includes extensive sections where the underground cables run through cable conduits. Implementing these works typically requires heavy construction machinery for earth-moving, pipe handling and dewatering and consumes large volumes of construction and auxiliary materials. Against this background, civil engineering related to pipe laying is one of the areas which keeps trying to make the construction workflow more efficient by coming up with new construction machinery and techniques as well as by developing them further.
For Bohlen & Doyen, the focus has not only been on increasing efficiency, but also on developing and implementing economic and sustainable construction methods which can be used in the context of constructing transmission networks. The goal associated with carrying out the laying the protective pipe in the context of the Wahle-Mecklar project, section C6, was to speed up and simplify the procedures associated with the installation of protective pipes with regard to the aforementioned aspects.
With this goal in mind, Bohlen & Doyen decided to use its novel cable- and pipe laying carriage, the “KaRoSch” (which the company had recently developed and manufactures itself), on this pilot line near Göttingen for the very first time.
This cable- and pipe-layingcarriage makes it possible to integrate previously separate process steps, some of which up to now needed to be performed without mechanical support, thus involving arduous and physically demanding manual labour. The pipe-laying carriage completely eliminates the need for the lower pipe bedding, which is conventionally installed first using a Delta Loader with Minigrader to match the profile. Also, thanks to this innovation in the field of laying methods, skilled workers who used to be needed in the pipe trench for the purpose of placing the pipes as well as to align and position the pipe string along the templates, can now be employed elsewhere. Also, the adding in of the bedding material and compaction via vibratory plates are among the process steps which can be performed as a single step thanks to the KaRoSch.
As a result, the laying procedure no longer involves staff in the pipe trench performing various kinds of work there, which constitutes a significant improvement both to the operational safety of the colleagues in the pipe trench as well as with regard to labour- and equipment cost.
Moreover, the KaRoSch offers significant advantages regarding environmental impact and resource efficiency. Compared to the commonly practiced open-trench installation, it reduces the time period during which the pipe trench remains open to just a few minutes. Depending on the existing soil conditions, dewatering measures can thus either be minimized or be done without completely.
Making the trench profile match the KaRoSch geometry, together with the built-on technology in the cable- and pipe-laying carriage, saves considerable amounts of bedding material (up to 20 %). In addition to the modified trench geometry, the profile haul-off plates as well as the layout of the compaction unit make sure that no excess bedding material is fed into the trench. Thanks to state-of-the-art technology, the compaction unit runs on rechargeable batteries. Since the equipment is only used for short time intervals at a time, they usually last for a full workday. This way, the cable-laying carriage as such does not produce any exhaust emissions. Moreover, this technology eliminates the risk of environmental harm in the event of a potential damage, since the equipment does not require any water- and soil-endangering consumables.
All in all, using the KaRoSch in the process helps to significantly reduce any interference with nature by reducing excavation volumes as a result of minimising the trench cross section, as well as in view of the short time period for which the trench remains open and the perfectly matched technology.
The development and application of the novel KaRoSch in the context of the project was the culmination of the successful development, construction and production of an efficient cable- and pipe-laying system at Bohlen & Doyen Bau GmbH. Process simulations and preliminary testing including comprehensive documentation had helped to optimize the application of the unit.
Its deployment at the construction site revealed that optimally coordinated preparation of the individual work steps is fundamentally important for a successful use of the KaRoSch. In this context, a smooth supply chain related to delivery of the bedding material is vitally important. The advantages provided by the KaRoSch are particularly significant when dealing with mostly straightline segments devoid of any crossing obstacles. Compared to the conventional installation method, the KaRoSch achieves a laying speed which is up to 25 percent higher due to its simultaneous laying of the six pipes as well as its outstanding adaptability and, most of all, thanks to the integrated compaction technology.
It was particularly important to the grid operator TenneT to be able to use the KaRoSch on locations on a slope that made the regular trench of the open laying method impossible, or in very moist soil structures, which makes extensive dewatering, as would be necessary in the open cable trench, obsolete. In the course of executing the project, we have been able to gain many insights which will help us optimise some aspects of the KaRoSch even further. Thus, Bohlen & Doyen will be able to refine the system with a view to future applications, e. g. also for other bedding materials and pipes.