The requirements for a nationwide and simultaneously flexible power network are higher than ever before, from an economic and ecological point of view.
The challenges in expanding and maintaining a complex infrastructure are continuously growing, especially in times of increasing networking and energy transition, with regard to service line capacities, operating ranges and service security.
Here, the underground construction method offers power producers and suppliers intelligent solutions for a careful and efficient installation of protection pipes and cables, as well as for the production of connections at the end users.
This report describes the various tested trenchless methods for underground cabling, as well as the latest machine technology developments, and also illustrates the functions and advantages by means of practical examples.
- Advantages of the NODIG technology
If you consider that up to 80 per cent of the investment costs for conventional open trench pipe installations fall on civil engineering, then the cost saving potentials are easy to imagine when applying the trenchless method.
The various underground methods, which are summarised under the technical term “NODIG technologies”, are so far developed and tested that all types of pipelines can be installed, quickly, carefully and cost-efficiently up to the connection at the end user.
The trenchless methods do not only have economic advantages as opposed to the open trench method, they are clearly more environmentally friendly and socially compatible.
The main benefits are clear to be seen:
- Valuable surfaces and resources are protected, as extensive excavation and reinstatement work is not necessary
- Hardly any disturbances for local residents and the business traders, no interference of the urban quality
- Hardly any traffic disturbances, follow-on damages to road surfaces are prevented
- Immense reduction of environmental damage, therefore clearly less emissions and consumption of natural resources
- Short construction and set-up times, quick construction execution, high adherence to time schedules
- Target-precise and reliable technology, process-reliable and proven application
- Maximal planning and technical security through high regulation conformity
- Immensely lower direct and indirect costs compared to the open trench method
- Trenchless solution for the power supply
The supply of electricity requires a dense and flexible power network. The challenges mainly arise through the ever-growing capacity requirements, which involve the development of renewable energies, the oscillations in the power generation and loads on the networks.
For example, in order to transport wind power from the wind energy plants onshore and those offshore in the North and Baltic Sea, it is almost unavoidable to install new power cables.
Long-term discussions and disputes, whether to install overhead lines or underground lines for new extra-high voltage lines often delay the power being provided to where it should be, as quickly as possible.
Nowadays, more and more power networks up to 110kV are being installed underground, as this increases the operating reliability and lowers the costs for the continuous operation.
However, underground cable installations with the open trench method involve high costs and long construction times. This is where the underground construction method offers innovative and lasting solutions for the installation of protection pipes, for the power supply of all voltage levels and for transport and distribution.
With the trenchless technology, a secure ground cable installation is practically possible anywhere: in complex urban areas or in the countryside, in protected areas or under inshore waters. The required installation depths can be easily implemented.
The NODIG method, which is recognised by the environmental and conservation organisations as a sustainable method, allows projects to be realised which otherwise could not be carried out for reasons of natural protection or due to worried residents.
Power-house connections can be produced trenchless from a starting pit or a keyhole up to the building, or directly into the supply room inside the building and also in the opposite direction.
The application of the NODIG technology offers maximal planning and technical security, taking all relevant regulations (DIN, VOB etc.) into consideration and the precise verifiability of position, function and tightness of all new pipelines.
Outlook: NODIG technology for the e-mobility
In connection with the energy transition and the reduction of climate-damaging greenhouse gases, the extension of the e-mobility plays a key role.
However, the acceptance of e-mobiles by the general public depends on a sufficient quantity and a comprehensive widespread of loading possibilities.
Even here, the NODIG-Technology offers intelligent and economical solutions for an efficient and low-emission extension of the charging station infrastructure.
Depending on the connection length, quantity and capacity of the charging stations, soil displacement hammers, as well as midi and mini-bore rigs for the underground cable protection pipe installation are applied, usually up to ND 160mm.
The possibilities include:
- Quick and careful underground installation of protection pipes for power and control cables from connection point to charging station and between the charging stations (sub-distribution or connection to distribution network)
- The connection to the power supply of the charging stations can also be guided trenchless into the connection room inside buildings
- With the minimally-invasive keyhole method the circular starting pit is used as a foundation for the charging station
- The listed trenchless technologies are equally economic for the installation of single charging stations and serial installations
Versatile NODIG method for transport, distribution and connections
For the underground installation of cable protection pipes and the production of house connections, various trenchless methods are applied, depending on the general conditions.
There is a differentiation between non-steerable and steerable installation systems. Non-steerable bore devices, such as a soil displacement hammer, are usually applied over shorter distances, if the bore path is a straight line.
This is also the case for steel pipe installations with the ramming method, which can cross beneath roads and railway tracks over shorter distances, but can also supply an optimal solution to install power pipelines for underground cabling, e.g. construction of bore path passageways for wind energy.
The installed steel pipes are suitable for all power types and work with 380,000 Volt alternating current transmission (also known as three-phase current), as well as high-voltage transmission.
With steerable horizontal bore rigs (HDD systems) of the midi-class, where the bore process can be tracked precisely with modern detection systems and, if necessary, altered even in combination with the larger bore rigs in the maxi-class, the high-temperature resistant plastic pipes, generally up to maximally 250mm diameter for HVDC links or three-phase conductor circuits (alternating current transmission) over longer distances along straight or flexible bore paths can be installed.
The utilised construction area is much smaller in this case, than with the open trenching method and only necessary in the starting and target areas.
Depending on the general conditions, various trenchless methods are suitable for inner-city distribution or access networks, ranging from the soil displacement hammer to midi and mini class bore rigs for the installation of protection pipes to the production of connections directly into the supply room inside the building.
All methods have one thing in common, they can be applied for almost all soil classifications, up to and including rock.
3.1 Non-steerable NODIG method
3.1.1 Soil displacement method with the soil displacement hammer
With the soil displacement method the pneumatically driven soil displacement hammer drives open an underground bore hole in which short pipes with smooth sockets and long pipes up to ND 180 mm or cables can be pulled into over short distances, either immediately or laterally.
As a head access hole is not required in front of the building and the soil displacement hammers can be started directly from the inside of the building, the soil displacement method is ideal for the production of house connections.
3.1.2 Dynamic steel pipe installation with horizontal pipe rammer
If the required overlap for the soil displacement method is exceeded, the steel pipe ramming method is applied, in which open steel pipes without abutments are driven precisely through the soil with dynamic ramming energy.
This way, steel pipes up to ND 4000 are installed beneath roads, railway tracks, parks, trees and buildings, vibration-free and without any danger of soil settlements. The soil penetrating into the pipe can be pressed out or drilled out with air and/or water after completion of the installation.
- 2. Steerable NODIG method
3.2.1 Horizontal fluid-assisted method (HDD) with steerable bore rigs
With the horizontal fluid-assisted method a steerable HDD bore rig is applied to initially produce a pilot bore along a flexibly plannable bore path.
When pulling back the drill rods, the bore hole is enlarged with an expander head and the connected pipe pulled simultaneously into the bore path.
This way pipelines can be installed along curved paths beneath roads, railway tracks, rivers, buildings or along straight bore paths.
As large pipe diameters can be installed along flexibly plannable bore paths this way, the horizontal fluid-assisted bore method is suitable for the extension of pipe networks within complex inner city infrastructures, as well as in countryside areas.
In tight spaces, or for house connections in hillside locations, beneath staircases, walls etc, which can not be produced with a soil displacement hammer, bores can be carried out with smaller bore rigs, so-called Mini-HDD Systems.
3.2.2 Keyhole technology
The minimally invasive keyhole technology was developed especially for serial installations of house connections.
With this especially gentle type of steerable bore, house connections are installed from the main line, out of the smallest possible circular assembly pit (keyhole Ø 65 cm) directly into the house or into a small assembly pit in front of the house.
The keyhole is produced beforehand with the coring and suction excavator technology and in doing so, exposing the main line.
All connection work is carried out aboveground with special telescopic tools and the keyhole, together with the excavated bore core, reinstated later, tension-free, without any additional asphalting work necessary, or any consequential damages.
The innovative keyhole technology is also optimally suitable for the installation of standalone charging stations for e-mobility, by using the round pit (keyhole) as a foundation for the loading station.
A further advantage is the production of the connection (with foundation and fixation plate) can be carried out at a separate time from the assembly and the launching of the charging station.
Furthermore, the set-up place can be chosen very flexibly, as bores can be carried out in any desired direction and length.
NODIG technology for the power supply in practice
The advantages of the efficient NODIG technology come into effect in economic and ecological respects, not only for the installation of transportation pipes, but also for the production of distribution networks and house connections.
The functionality and advantages are better illustrated through single practical applications. We would like to show some practical examples for all these applications on the following pages.
4.1 Application example: Multiple river crossings with the HDD method for a fast power supply
In Stockach, near Lake Constance, a river coming from the Oberschwaben region had to be crossed under several times in order to install a new power cable.
The municipal energy supplier, Stadtwerke Stockach, operates the power network there with ca. 4,900 monitoring points.
Around 8,000 inhabitants, as well as 650 industrial and trading customers are connected to the power network. In order to guarantee a secure supply and the requirements in the ever-growing community, a second control plant was built in 2015, connected directly to the power substation for the network, via a 1,500m length feeding line and the Stockach metropole is now supplied parallel via the two control plants.
The bore path for this new medium voltage cable crossed beneath the River Aach in Stockach at four different places. In each case the GRUNDODRILL HDD bore rig was applied to cross beneath the river with the pipes for this installation.
The geology in the area was a special challenge, as the ground consisted mainly of pebbles and rubble from the ice age.
Thanks to the high pulling and pushing force of the HDD bore rig with approximately 25t and the special tools, designed for rocky ground, the trenchless installation work was completed without any problems whatsoever.
The pipe material was pulled into the ground in bundles, whereby the larger pipes were used to retain the single conductor cables for this new medium voltage cable and the control and data cables were pulled into the accompanying 50mm pipe.
Apart from a few sandstone obstacles close to the weir level of the river, which slowed the bore process down slightly, all bores were carried out in a routine manner, despite the difficult geology and within the planned time schedule.
After four weeks, all four bore paths were completed and presented to the surveying technicians of the public service company to carry out their measurement process.
4.2 Application example: Switchover from overhead cable to underground cable with HDD technology
In Malente-Kreuzfeld, in the Schleswig-Holstein region, the access route in the Plöner Street to the company Kies-und Schotterwerk (Gravel mill) Kreuzfeld GmbH needed renewing and widening.
The building contractor Schleswig-Holstein Network AG saw this as an appropriate opportunity to convert the power supply to an underground cable installation, which up to now, had been provided via an overhead line.
The protection pipes for the power cables were to be installed, for logical reasons, underground with the HDD method. The Schleswig-Holstein Network AG appointed the company TMW GmbH/Volker Tantow to carry out this project.
They in turn appointed Paasch Pipe Installations GmbH & Co. KG, who has been experienced with the HDD technology for many years, to carry out the installation of the HDPE protection pipes, ND 125 with the horizontal fluid-assisted method (HDD).
With this task and the typical sandy and loamy soils in the Schleswig-Holstein region, zero hour arrived for the first true application with a new HDD bore rig, Type GRUNDODRILL JCS130.
This new generation of horizontal fluid-assisted bore rigs distinguishes itself with an increased degree towards an intuitive operating concept, as well as its demand-oriented, modular design, which make the application of the HDD method even more efficient and profitable.
The extensive automation of all sequences allows for example, for the first time, remote-controlled bores with an innovative remote control, developed in-house.
The length of the first bore was over 93m and the second bore over 100m.
After each pilot bore, carried out with a Medium Drill Head Type 1, diameter 100mm, the expanding process, with a stepped reamer up to 200mm, was carried out, simultaneously pulling in the PE-protection pipe ND 125. Despite the tight working conditions, which the normal working operation at the adjacent gravel plant with heavy truck traffic brought with it, the bore rig hardly caused any “disturbance”, due to its particularly small working width of only 1.85m.
Each of the three bores and pulling-in processes for the protection pipes were completed within one day, to the fullest satisfaction of the participants. The gravel mining was not interrupted at all, due to the compact jobsite set up and also maintained throughout.
4.3 Application example: Five house connections in two days with a soil displacement hammer
Landsberg on Lech is a town situated on the famous Romantic Road and a main tourist destination with its well-preserved middle-aged town centre.
However, the town has also arrived in the modern world and acts farsighted and visionary when making key decisions. This was also the case for road construction work on the Hindenburgring, a four-lane bypass of the old town.
The public utility company Stadtwerke Landsberg and the municipal civil engineering office have coordinated their work accordingly in the course of extensive redevelopment measures on the footpath and cycle path in this area.
The road disruption was used to good effect to renew the outdated house connections for the power supply along this path, in fact with an environmental -riendly method. The local company E.K.L. Cables and Installations GmbH was booked to carry out the task.
The civil engineering company is a specialist for trenchless installations and has counted for decades on the soil displacement method, using soil displacement hammers and equipment for direct pipe installations and with great success.
The environmentally-friendly trenchless installation technology was clearly the obvious choice for installing new power/house connections at the Hindenburgring in the city and on the busy road.
The decision was also influenced by the necessity to cross beneath existing fence foundations, cobblestone areas, as well as hedges and gardens, some even with very old trees and plant vegetation.
The nature of the compact gravel underground ultimately forced the decision on the equipment to be used: a 75mm GRUNDOMAT Soil displacement hammer of the new generation with crowned head.
The lengths of the new house connections, in this case the lengths of the single pilot bores, had varying lengths, due to the distances of the houses to the main power line: 6m, 11m, 5m, 8m and 4m.
Working from a small starting pit, the pneumatically driven GRUNDOMAT Soil displacement hammer 75mm (two-gear control unit plus reverse gear) with crowned head, worked target-precise, with running stability, reliably and effective in a depth between 0.6m and 0.8m on each predetermined bore path through the compact gravel.
The crowned head expanded the pilot bore directly to the required bore diameter and the 63mm PVC installation pipe to retain the power cable was pulled in effortlessly with the PVC direct installation equipment.
As described above, the maintenance and expansion of all types of power networks can be carried out considerably more efficiently and environmentally friendly by applying NODIG techniques for underground cable installations.
Furthermore, the costs can be significantly reduced for a demand-oriented and high-quality service line infrastructure, compared to the open trench method – with maximal supply reliability, but without deterioration of valuable surfaces and follow-on costs.
The recording of all trenchless methods in the relevant book of regulations guarantees a further maximum safety in the planning and execution of underground pipe installations and renewals. Interested suppliers/planners can obtain further information from industrial associations such as the Pipe Installation Association (rbv), the German Society for Trenchless Technology (GSTT), and specialised civil engineering companies and manufacturers.
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