Alternative installation methods: opportunities for rapid expansion of the digital infrastructure

Comprehensive connectivity by 2030: alternative laying techniques are to be used to accelerate the expansion of fiber optics in Germany

According to the Breitbandatlas der Bundesnetzagentur, around 96 % of German households had a broadband connection in mid-2023. Around 75 % of these were gigabit connections, of which the proportion of pure fibre optic technology (FTTB/H) was over 28 %. In addition to the German government's Gigabit-Strategie, the EU Commission's Gigabit Infrastructure Act (GIA) of March 2023 is also intended to contribute to an accelerated, nationwide expansion of the high-speed network by 2030. Among other things, its regulations aim to standardise conditions and reduce costs during implementation as well as - where locally possible - the shared use of physical infrastructure. Meanwhile, DIN 18220, which was published last July, is intended to provide more legal certainty on German construction sites. This regulates a number of alternative laying methods that had not previously been standardised for fibre optic expansion. Which techniques are involved and what practical experience can already be drawn on?

1. Fibre optic technology briefly explained

In contrast to the copper lines of DSL and cable internet, which transmit signals electrically – and therefore lose bandwidth and speed over longer distances – fibre optic technology enables very high transmission speeds of up to 1000 Mbit/s. It uses so-called fibre optic cables (FO cables).

Structure of fibre optic cables and signal transmission
Fibre optic cables are fibres made of plastic or quartz glass. They transmit incoming light signals (optical signals generated by laser diodes) as a light-conducting channel by means of reflection and in this way transport them from the transmitter to the receiver.

Several optical fibres are bundled together in an optical fibre cable. Each strand consists of four different layers:

the hair-thin fibre core that transports the optical signals,
the quartz sand cladding that encases the fibre core and enables total reflection,
a flexible and protective plastic coating,
a particularly robust outer protective layer made of plastic or metal.

Material properties
Due to their nature, fibre optic cables are insensitive to electromagnetic interference and temperature fluctuations, unlike copper cables. Due to their fragile architecture, however, the wafer-thin glass fibres can break easily and must therefore be laid without tension or force.

Fiber optic technology: Fiber optic cables enable transmission speeds of up to 1000 Mbit/s

Alternative laying methods for fibre optic projects

As part of its Gigabit-Strategie, the Federal Ministry for Digital and Transport (BMDV) named various alternative laying methods for accelerating the expansion of the fibre optic network in a key points paper published in 2022. These have been enshrined in DIN 18220 since March 2023. The majority of the laying techniques that can be used in fibre optic construction differ from those that are usually used in open underground pipeline construction, with regard to depth, type of execution or the tools used for example. In addition, according to the above-mentioned key points paper, it should be examined whether "feared expansion risks or unexpected structural damage arise in connection with the use of newer installation methods and can be mitigated if necessary." For trenching methods for example, in 2020 the BMDV already cited "changes in the level of the road structure due to soil displacement or the effects of use as well as frost or compaction damage" as possible disadvantages of these methods.

Laying in open construction method: Cable ploughing and trenching methods
The cable ploughing method uses a plough that is pulled through the ground by a tractor. The empty conduits are laid in the gap created in this way. This method can only be used outside built-up areas along roads and on unpaved routes.

The so-called "shallow laying" (see DIN 18220) using trenching includes various techniques such as milling, sawing and grinding, depending on the subsoil. Depending on the method, soils, roads or paths are provided with trenches or slits 10-50 cm deep and 2-30 cm wide and then sealed again after the cables or pipes have been laid.

Trenching using a milling cutter is one of the minimally invasive installation methods

Laying in closed construction method: Horizontal directional drilling method, soil displacement method, laying in the sewer
In trenchless construction, an underground bore channel is created between the start and end points of a pipeline. Depending on the location and nature of the subsoil, different methods can be used.

Horizontal directional drilling methods allow cable ducts to be laid up to a depth of 10 m and a length of up to 500 m. In confined spaces, smaller excavation pits and shafts (such as for house connections) or short crossings, the mini-flush drilling system is used as a variant. Similar to this is the keyhole method, a keyhole technology that minimises intervention in the earth's surface before cables or pipes are pulled in using telescopic tools.

Only one person is required to operate the fully automatic GRUNDOPIT KS50

In soil displacement methods, either a so-called soil rocket (uncontrolled soil displacement method) or a steerable steering head (directional pressing method) is driven through the soil before a cable conduit is subsequently pulled in in the outward or return direction. Both techniques are used to create house connections and short crossings.

When laying in the sewer, existing infrastructure can be used for fibre optic cables, depending on the existing infrastructure and approval requirements. Empty conduits or cables can either be laid directly in wastewater systems or integrated there as part of sewer renovations. Both active and decommissioned sewer systems, which do not necessarily have to be accessible, can be considered.

Use of an earth rocket at the fiber optic practice day in Großbottwar, Baden-Württember

Methods of above-ground installation
If, especially in rural areas, smaller settlements or districts are to be connected to existing underground cable routes, for example, above-ground installation on the pylon (extension of existing infrastructure or new construction) can be considered. Junctions/branching points or feed lines to properties as well as large distances can be efficiently connected or bridged in this way.

From the field: "Road construction authorities exchange experiences"
An interactive platform created by the Federal Gigabitbüro at the end of last year provides representatives of local authorities with information on practical experience with fibre optic expansion. "For this purpose, road construction authorities were specifically asked about previous experiences, working methods and information about the entire process from the enquiry to the construction supervision of the alternative laying methods," as it says there.

As of 24 January, around 90 municipalities from various federal states across Germany had shared their practical experience, 70 % of which reported from rural areas and 30 % from urban or semi-urban areas. If we focus on the information on laying techniques, the flush boring method leads the field with 40 %, the ploughing method with 21 % and the trenching/milling method (bonded superstructure) with 15 %. Only 4 % of the construction contractors provided information on experience with above-ground laying.

3. Public discourse

DIN 18220
The standard essentially defines "for the first time clear conditions of use and execution for the alternative laying methods of raking, ploughing and milling". Other tried-and-tested techniques (such as trenchless laying) are not taken into account - a point criticised for example by the Bundesverband Breitbandkommunikation e.V. (BREKO), which emphasises that the standardisation of individual techniques in municipal approval procedures should not reduce acceptance for the use of other, tried-and-tested methods.

Possibility of overbuilding
The topic of overbuilding also dominates part of the public discourse on broadband expansion. The Gigabit Infrastructure Act (GIA) obliges network operators to grant competitors access to physical infrastructure (such as ducts). According to WIK Consult, "the economic effects of the publicly discussed cases of overbuilding are assessed very differently" by market participants. As a result, an economic analysis and legal categorisation of the market situation was carried out in a WIK study published on behalf of BMDV 2023.

Recruitment of skilled labour
Demand for skilled workers is also high in the fibre optic market. According to the Federal Government's Gigabitbüro, there was an increase of 25 % in the first quarter of 2023 compared to the same period last year. The majority of advertised positions were unfilled at this time.

Special job exchanges or targeted training and further education initiatives - such as the joint "Initiative Fachkräfte für den Glasfaserausbau" of the BMDV and the Deutsche Industrie- und Handelskammer (DIHK) - are intended to remedy this situation. The "Initiative Gremienverbund Breitband" (IGVB) has developed a multi-stage training concept with uniform standards and published it in the form of VDE guidelines. The training providers listed there - such as the Berufsförderungswerk des Rohrleitungsbauverbandes (brbv) - are part of a modular qualification network. The aim is to close the gap in the labour market by offering numerous training courses or courses that build on each other, ranging from basic knowledge to technical specialisations.

4. Conclusion and outlook

According to the above-mentioned state actors, the use of alternative laying procedures currently appears suitable from a (time) economic point of view for accelerating the expansion of the German high-speed network. It would be desirable to find a consensus quickly in the event of existing disagreements between market participants in the context of the double expansion discussed above. If it were also possible to close the skills gap in the labour market in the medium term, this would undoubtedly benefit the goal of achieving nationwide fibre optic connectivity by 2030.