Master plan for a sustainable supply and disposal infrastructure of mega cities - Part III

General
As described in the previous, second part, the utility tunnel does not only solve many of the presented problems but also provides the most economical solution if such structures are considered within the scope of a generation contract. Apart from all advantages, such concepts must be integrated into the already existing and highly used underground infrastructural space. This produces great demands on the construction process. A short overview of the possible technologies is presented in the following.

Method of construction
In operation, the structural shell of the utility tunnel has the following functions:

• Withstanding the external loads
• Sealing against seepage, pressure and precipitation water, roots as well as external influences.

It is primarily constructed of reinforced concrete. This makes a multitude of types of construction available which differ especially in the degree of prefabrication (locally manufactured and partly or wholly prefabricated).

Prefabricated parts (pipes (Figure 1), box profiles or assembled components) usually offer advantages when the same cross section can be used over long distances. If, however, there are many constraint points in the course of a line that often require cross-sectional displacements, or if the utility tunnels are very large, then the in-cast concrete method of construction has the advantage also of fewer joints. In addition, the transport distances and the transport possibilities play an important role in the choice between the prefabricated or monolithic in-cast concrete method of construction. Furthermore, a combination of the in-cast concrete and prefabricated method of construction in the form of the mixed method can make use of the advantages of both manufacturing variants.

The following variations are available for the execution of the construction itself:

• Open cut method: The open cut method is characterized by the excavation of a pipe trench, creating the structure in the protection of a slope or a lining and then filling the excavation again.
• The trenchless method: The trenchless method is characterized in this case by an underground creation of the utility tunnel. The path can be accessed via starting and target shafts. In the trenchless method, the utility tunnel, depending on the selected method, can be constructed by the jacking of pipes of larger nominal size (Figure 1), by shield tunnelling with segmental linings (Figure 2) or by tunnel and gallery headings with subsequent installation of an inner shell of in-cast or spray-on concrete or by means of reinforced concrete prefabrications in the opened cavities.
• Semi-opened method of construction: the semi-opened method of construction is an intermediate method between open-cut and trenchless methods of construction. It is basically suitable for the installation of prefabrications with a closed cross section, i.e. of pipes or box profiles.

Cross section and arrangement of the excavated utility tunnel
Laterals, also called service pipes, are understood in this case to be lines which lead from the connection point of the supply pipe or the sewer in the utility tunnel through the structural shell (wall) to the user.

The installation of the lateral can be carried out at the same time as the creation of the utility tunnel or at a later time in the open cut or trenchless method of construction taking the geological and hydro-geological limiting conditions into account.

Independent of the open cut or trenchless method, the variants of individual or multiple installation are available with reference to the use of the line.

The single installation in the form of underground installation and the installation in a casing pipe is contrary to the concept of the utility tunnel, as in these cases especially the access to the pipes for servicing, rehabilitation and operation is dispensed with.

The following variants of multiple installation of lines are advisable in this connection:

• Installation in a host pipe
• Installation in a utility duct
• Installation in a utility tunnel.

The variant of the installation in a host pipe has been used in the Federal Republic of Germany since the year 2000 in the installation of laterals to conventional network, e.g. by the use of the so-called multi-section building inlet (Figure 3).

Power and telecommunication as well as water and gas pipes are fed into special empty pipes and inserted as a bundle through openings in the building structure. The advantages of the multi-section building inlet over single installation are:

• Time-saving by coordinated execution
• Customer-friendly due to a reduction of contact persons
• Place-saving due to a central wall or floor plate entry point into the building
• Cost reduction – only one pipeline trench for all supply lines on the private property
• Later pushing-in of the supply lines through colour-differentiated empty pipes into the house possible.
• Trouble-free replacement of the supply lines through the empty pipe system.

From the point of view of rehabilitation, the ideal solution is the installation of the service pipes in a man-accessible utility tunnel or in one in which one can creep that reaches from the utility tunnel to the house. The ownership and responsibility border in this case could lie at the interface between the utility tunnel and the building wall. The lines at this point should pass through a fire wall. Entry and exit to the utility tunnel by authorized persons could be made possible, if desired, through the installation of lockable doors or manholes. From the point of view of security, especially acts of sabotage, this variation is the worst one as this utility tunnel permits relatively quick unauthorized access to the piping system.

Alternatives to Multiple Installation in the Utility Tunnel
However manifold the applications of a utility tunnel may be, there will always be limiting conditions that make its use uneconomical. However, this does not mean the return to the single installation of sewers and pipelines; it rather leaves the door open for further alternatives in the form of multiple installation.

Alternatives to multiple installations in the utility tunnel are the multiple installation in a host pipe, in a utility duct and in a man-accessible sewer.

Host Pipe
Host pipes are underground non-man-accessible or man-accessible pipes for later installations of several product lines or casing pipes of the same or different types. Host pipes are not accessible to people after the installation of all lines (final installation).

The following variants are noted (Figure 4):

• Loose installation in the host pipe
• Bundled installation in the host pipe
• Group installation.

Multiple installation in a host pipe is used today exclusively for installation beneath traffic lines and waterways with the aid of trenchless installation. It has not yet been used as a solution variant for the complete inner-urban infrastructure. It is feasible to use this concept, for instance, in the installation of telecommunication networks and/or electrical supply systems.

In the loose installation of lines, usually cables, they are either pulled in or blown in individually or together in one working step. Here the adherence to line spacing and arrangement is purposely dispensed with in order to have the possibility in the future to replace a single line by pulling it out.

In bundled installation, the lines are tied together at particular spacings by means of plastic adhesive tape, cable binders or slides. In this way a controlled guiding of the individual lines and adherence to specified external bundle diameters is more or less ensured. A later replacement of individual lines is not possible.

In group installation, the individual product and casing pipes are arranged and fixed by means of multiple shells or spacers and inserted into the host pipe with the aid of rollers or skids. The spaces can then be filled if required.

If the spacings are not filled, the host pipe must protect the lines from outside influences and act as a casing pipe in the case of failure of the product pipe(s).

Utility Duct
Utility ducts are underground installations for ordered installation of supply and discharge lines using the structural shell for fastening the lines or supporting them with the aid of wall plugs, multiple fasteners or pipe supports. In order to obtain later access to the lines, the remaining space is not filled.

In the operating condition, the utility duct has the following functions:

• To withstand all external loads such as earth and traffic loads, water pressure, plane loads, strip loads, point loads,
• Sealing against seepage, pressure and rainwater, root growth as well as external influences,
• Acceptance of the planned lines according to number, type and dimension,
• Ensuring the operational needs as regards the installed lines, including gradients, expansion, venting, flushing, micro-climate and prevention of mutual influences.

Utility ducts can be designed to be non-accessible or accessible as desired (Figure 5). In the operating condition (final installation), both variants are not accessible to personnel due to the full utilization of the available cross sections.

Man-Accessible Sewer
The use of man-accessible sewers for the multiple installation of other lines is no novelty. The sewers of Paris (Figure 7) have served, since their installation in the 19th century, also for the accommodation of water and compressed air lines which are situated in the upper part of the sewer which remains free even at maximum flow of the cross section designed to be man-accessible. This variant is currently the subject of an investigation being carried out by the engineering consultancy of Prof. Dr.-Ing. Stein & Partner GmbH, Bochum, with the aim of developing new combined residential and business regions.

Conclusions
In the 21st century, the city will be the most important place of residence for people. The qualitative as well as the quantitive demands this makes on the technical infrastructure of the city will present an enormous challenge to the urban and regional congested areas all over the world for a long time in order to ensure a secure and adaptable supply of water, gas, electricity, district heating, modern telecommunication services, etc., as well as the provision of an environmentally friendly disposal system.

As experience in Germany and Europe has shown, the system of single installation of the various line systems in the cross section of the road in use since the 19th century is not suited for filling these demands on a sustainable level.

Thus we need to discard the assumption that these life arteries of our settlements function as a matter of course and will continue to function when above them rebuilding or closing down takes place or when there are drastic user changes from the original user estimates due to saving measures, growth or a reduction of the population. This will become clear in the water saving measure or the substitution of drinking water on environmental grounds within the scope of the European Water Charta of May 6th, 1968 – a worldwide necessity which has already been recognized and taken into consideration by the German government and whose potential has not been exhausted by a long way – as well as the seepage or utilization of rainwater. These needs resulting from the constant change and development of society are already leading to substantial problems in the operation of the water supply and discharge networks which cannot be solved without massive interventions and thus in the short term.

We must also discard the assumption that the technical infrastructure of the city, once installed, will function until the end of its useful life without regular maintenance measures (inspection, maintenance and rehabilitation). In the future, these measures will also feature prominently in politics and will thus cause relatively high costs that will increase as the system ages as all these measures have a high degree of difficulty with directly installed pipes.

The competitiveness and capabilities of a city not only depend on the quality and the design of their aboveground environment but also on how far today still unknown line systems can be installed quickly, cheaply, environmentally friendly and especially without disturbance of the already existing networks, streets and traffic. In this connection it can already be seen today that in the future more and more new and more efficient communication cables will need to be installed, or one day perhaps even transportation pipes for underground goods transport [6], transport pipes for disposal of rubbish from households [7] and the presently discussed pipe systems for creating new substance circuits such as the collection and draining of yellow water as a resource for phosphorous mining.

In summary it can be said that the concept followed up to the present of single installation of pipes in the cross section of the road massively hinders all the measures described above and makes it impossible for the supply and discharge undertakings to

• adapt their networks in accordance with the customers wishes
• to react simply to new technical developments and
• to integrate new lines into the overall system.

It is time to think about our line networks and not only for the reasons given above but because of the fact that many network operators, in recognition of the huge market potentials, are giving up their branch approach and, for instance, are using sewers as a path for communication cables or are tending to operate the supply and discharge systems of our communities in the widest sense as an overall task and thus to use the synergy effects of the various networks. In recognition of the linkages between the line networks and the changing user structures, sustainable systems are required that fulfil the requirements of the present without limiting future generations and forcing them to constantly build new networks.

The positive experience that have been made in Switzerland in the installation of supply and discharge lines in utility tunnels and the negative experience in the course of the rehabilitation of sewers in Zurich have caused the previous leader of the Civil Engineering Office of Zurich, Prof. R. Heierli, to make the following statement 1990 [8]:

"If one were to design a city today, then one would doubtlessly install most of the lines in man-accessible utility tunnels."

Depending on the requirements, utility ducts can be made to be man-accessible or non-man-accessible for the construction state. In the operational state (end of installation), they are in both cases non-man-accessible because of the full utilization of the available cross section.

For utility ducts that consist of pipes with non-man-accessible cross sections the lines (in present applications these are mainly telecommunication cables) are fastened with the aid of robots to the pipe walls.

At present, two processes are in use that are differentiated in the type of cable fastening:

• ­Drill and dowel method,
• ­Clip ring method.

The application of drill and dowel robots ranges at present from pipe sizes DN/ID 200 to 1200 [9]. The dowel spacing is usually 1.00 m.

The following piping materials are particularly suitable for doweling [10]:

• ­Vitrified clay,
• Concrete,
• ­Fibre cement,
• ­Polymer concrete,
• ­Plastics (PE) with fusing techniques (dowels are fused in place).

The area of use of the material-independent clip ring method ranges from DN/ID 200 to DN/ID 700 [11]. With a spacing of approximately 2 m, the clip rings can carry telecommunication cables as well as cable casing pipes

Bilbiography

[1] Holzmann AG Frankfurt: Fördertunnel Kiel. Tiefbau-BG (1993), Vol. 4, 216-221.

[2] Company information Takanaka Civil Engineering & Construction Co. Ltd., Tokyo, Japan.

[3] Company information Doyma GmbH & Co., Oyten.

[4] Stein, D.: Grabenloser Leitungsbau. Berlin: Ernst & Sohn, 2003.

[5] Adolph, H.-J., Schwebler, R.: Planung und Errichtung eines ca. 450 m langen, nichtbegehbaren Versorgungs-/Energietunnels (Düker) im Bereich des Neckar in Heidelberg. FGR Gussrohr-Technik 33 (1998), 14-19.

[6] Stein, D.; Schoesser, B.: CargoCap – A Vision becomes Reality. Tunnel (2002), issue 3.

[7] News release: Barcelona transportiert Abfälle unterirdisch. Zeitung für kommunale Wirtschaft (ZfK) (2003), October.

[8] Heierli, R.: Planungen mit Ver- und Entsorgungsstollen. Dokumentation ATV-Workshop „Undichte Kanäle“, 1990, 73-91.

[9] Company information JT elektronik GmbH, Lindau/Bodensee, Germany.

[10] Beyer, K., Röling, M.: Was haben wir gelernt? – Zwei Jahre Kabel in deutschen Kanälen. bi-umweltbau (2000), Vol. 2, 48-52.

[11] Company information KA-TE System AG, Zurich Switzerland.

To read Part I of this article series, please click here.
To read Part II of this article series, please click here.