The objective is to counter frequently mentioned reservations about the use of underground ducts with well-founded statements.

Stakeholders who are confronted with reservations about the use of underground ducts should be provided with valid arguments, information, or empirical values to counter these reservations. The most frequent reservations, including a statement, are listed below. The organisations or persons who wrote the statement are indicated for further information or contacts.

An estimate of the frequency of the reservations can be found below the statement.

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Reservations and opinions

Investment costs and economic efficiency are different criteria for different time periods.

The (additional) investment in a line duct avoids several conventional civil engineering costs (earthworks/shoring/dewatering/traffic engineering/securing / compensatory measures / …) for the line owners if the lines are laid in the line duct in stages or staggered over time. There are also savings with trenchless construction methods for each medium.

The economic efficiency is determined over the years of operation depending on several framework conditions such as bundling of pipelines in one route, replacement flexibility, protection, and resistance to influences and impacts as well as sustainability, especially in the sense of avoiding indirect and social costs.

Sustainable financing of (critical) infrastructure assets is already a current shareholder motive among some utilities and lenders.

81% of the respondents have already been confronted with this reservation.

Since 2009, market regulation of electricity and gas has been applied in Germany in the form of incentive regulation (Incentive Regulation Ordinance ARegV). Within this framework, the calculation of the grid utilisation fees (fees charged by the electricity or gas grid operator for transmission) is carried out by setting a revenue cap (for the period of the five-year regulatory period; see ARegV §4/§7 or Annex 1). In addition to the network costs, the calculation of the revenues also includes the capital costs (imputed depreciation, return on equity, trade tax, interest on borrowed capital), which is intended to ensure the refinancing of the investment (considering the Electricity Network Charges Ordinance (StromNEV) or Gas Network Charges Ordinance (GasNEV).

In the case of conventional laying, the line owner generates a higher capital cost contribution and thus higher permitted revenues due to the larger investment volume than a comparable measure in the form of laying in the line duct (which subsequently also incurs rental costs, which are considered differently within the ARegV).

Insofar as the electricity or gas network operator and all other divisions are not only users but also owners of the line duct, the capital costs can influence revenues, provided that the asset can be allocated to the line duct.

38% of the respondents have already been confronted with this reservation.

User fees or rents generate income for the line duct owner or operator and enable balance-sheet-based management of the structural facility.

The rental costs are offset by avoided costs for the users (line owners), e.g. through reduced maintenance costs and flexible use of the installation space.

In addition, the municipality can compensate for the usage fees through financial incentives, e.g. by reducing the concession fee.

The payment of user charges between the owner of the line and its user has been common practice for a long time and is to be negotiated in detail between the contracting parties.

In the case of a cross-connected company, as owner and user of the line duct, these are essentially internal business settlements.

57% of the respondents have already been confronted with this reservation.

The customer structure in new development areas and their development says nothing about the economic framework conditions (see also a statement on reservation 1). In the past, such an advantage in development was mainly due to uniform ownership structures.

Insofar as the advantages of the line duct are used to develop the area, planning ranging from line bundling on main routes, and culverting at constraint points to house connection routing should be considered. In a variant analysis, a multitude of reasons must be considered, which are often to be found in site-specific and location-specific features.

76% of the respondents have already been confronted with this reservation.

A high density of house connections can be realised in a bundled connection duct, e.g. in larger buildings/factory buildings or in conventional underground installations. Trenchless methods from a starting pit or basement level to the line duct (destination) are possible installation technologies. For the initial development, the open construction method is also conceivable.

The specific additional expenditure per metre of sewer can prove to be cost-effective during the period of use if there is an above-average need for completion or replacement.

In inner cities / old towns with a high density of existing pipes or very narrow construction spaces, a change in the installation of all media is often associated with high construction costs.

47% of the respondents have already been confronted with this reservation.

Instructions in accordance with an operating regulation is necessary for staying or working in the line duct. For work in confined spaces, for example in individual shafts of the energy and water supply, specialist training and separate training courses are generally necessary, which are extended to the subject of an elongated structural system (line duct).

Many years of experience in implementing proper operation in line ducts show that a high level of safety can be implemented through efficient requirements and routines.

52% of the respondents have already been confronted with this reservation.

Conduits make sense in densely populated areas if, among other things, redesign processes of the transport and building infrastructure are to be expected in the following years. An above-average expense for the subsequent construction of sewers can then be offset by a potentially high benefit.

In general, as in the case of development projects, it is not a matter of area-wide application, but rather of long-term orderly and safe conduit routing in heavily occupied subsoil.

43% of the respondents have already been confronted with this reservation.

The inclusion of a sewer project in the overall consideration of a project generally requires all parties involved to look at long-term economic, resource-efficient, and ecologically beneficial solutions. In this context, the municipality and the utility companies are of particular importance. Compromise is not a primary objective, but rather the choice of a preferable construction solution that is sustainable in the long term.

85% of the respondents have already been confronted with this reservation.

The road authority and the property owners are of particular importance. For this reason, the supply solution of line ducts must be considered as a component of medium- and long-term planning. The public authorities must be confronted more strongly with the feasibility of sustainable supply and disposal solutions based on pipelines (see also reservation 8).

76% of the respondents have already been confronted with this reservation.

Methodological principles coupled with planning requirements have been considered or published for many years, e.g. in cost-benefit studies or division-related cost comparison calculations for energy or water distribution systems. These considerations can also be applied in a modified form to line ducts. A model by entellgenio GmbH is available for the preparation of a comprehensible and complex profitability analysis.

19% of the respondents have already been confronted with this reservation.

Despite sector-specific legal bases and the usual application of media-specific concession and permit law, there are legal design options for multiple laying in ducts.

The legal bases are not unclear but are rarely applied. For the operation of ducts, organisational forms of public and private law have been legally prepared and practised for decades.

52% of respondents have already been confronted with this reservation.

Effects and hazardous situations of mutual interference were examined using concrete examples. Depending on the parameters (pressure levels, voltage levels), appropriate protective measures are derived by means of a safety assessment within the new construction planning or by means of a hazard assessment in the event of significant changes during operation.

The existing situations on some canal sections provide the corresponding references.

61% of the respondents have already been confronted with this reservation.

As a matter of principle, prolonged stagnation in drinking water pipes (TWL) and thus contamination of the drinking water must be avoided. Pipes in sewers or basements of buildings can be exposed to higher temperatures if no ventilation regime prevents this. Hygienic problems arise, among other things, when the flow velocity is too low, or stagnation occurs over a certain period. However, this is not a problem of the duct.

Such conditions can be ruled out if the pipes (including flow velocities, and insulation of heating pipes) and the duct (ventilation regime) are operated properly. Many years of experience in this regard are available in many cities. Special experiences show that in 50 years of operation of TWL in accessible line ducts, no hygienic problems have arisen so far that could be attributed to the heating of the drinking water in the duct.

If, for example, drinking water does not flow in connection pipes for a longer period and the temperature in the line duct is not controlled, hygienic problems may arise. The utility companies react accordingly when drinking water pipes are shut down.

61% of the respondents have already been confronted with this reservation.

There are many years of engineering experience in how to protect underground civil engineering structures (i.e. also ducts) against aggressive and pressing groundwater and stratum water in the construction and operation phase. Concrete formulations, the dimensioning of reinforced concrete structures and the application of special technologies for such cases of use represent generally recognised rules of technology which, among other things, comply with the principle of durability, impermeability, and stability.

28% of the respondents have already been confronted with this reservation.

For the construction of ducts, a safety assessment must be carried out during the planning phase and repeated risk assessments must be carried out for the operation of ducts. The basis for this is provided by comprehensive safety regulations in the DGUV rules and regulations and the corresponding professional organisations.

Experience shows that the safety level derived from these regulations is constantly being improved in detail. After decades of operating line ducts, there are no known findings in the area of activity of the “Interessengemeinschaft begehbarer Versorgungskanäle” (IBV) (“Community of Interest in Walkable Line Ducts”) on typical hazardous situations that are above the risks of individual installation.

14% of the respondents have already been confronted with this reservation.

The consistent implementation of operating regulations, which clearly regulate the presence of people in line ducts, and the technical possibilities to prevent or detect foreign access, significantly reduce the risk of vandalism.

57% of the respondents have already been confronted with this reservation.

When planning ducts and dimensioning envelope structures, the goal is to use raw materials in a resource-efficient way over the life cycle of the building. In other words, the additional emissions during construction can be offset by avoided emissions over the service life of more than 80 years.

The development of building technology also shows energy-saving ways through material substitution, the costs of which are not yet generated as market prices. In addition, there are pilot solutions for energy saving or CO2 capture in large-scale plants in cement and steel production.

23% of the respondents have already been confronted with this reservation.

The cubic dimensions of a line duct result from the multiple laying of different pipelines in an optimised construction space and can only be compared with several individual layings in the same period. A cable duct offers a compact and closely spaced cable routing that can withstand any comparison with a stepped trench.

In the case of subsequent relocations, replacement or dismantling of pipelines, the encroachments (including trees, green spaces) are significantly lower. For the conflict potential root spaces vs. line trench, experience in the long-term operation of line trenches can be used.

95% of the respondents have already been confronted with this reservation.

The caveat gives the impression that cannot be substantiated in the international diversity of applications. However, it is recognisable that through a “lean” and hierarchically organised planning and approval process, e.g. on properties owned by a landowner, more practical examples can be found than in the moderation of diverse interests.

43% of the respondents have already been confronted with this reservation.

Several hundred kilometres of sewers are in operation in Germany that have a useful life of 30 years or more. Some of them were built using inferior materials, or not according to the current recognised rules of technology.

As a result, mainly due to the influence of surface, strata, and groundwater, as well as deficiencies in timely maintenance and a lack of responsibility, defects and damage have manifested themselves in isolated cases, calling into question the durability and stability of the overall construction. Such individual examples are sometimes more likely to be noticed than the largely long-term standing and traffic-safe use.

Status of work: September 2022