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

Oct 12, 2006

This is the first contribution of a three-part series that deals with the following approach: "Master plan for a sustainable supply and disposal infrastructure of mega cities". It is motivated by the fact that, due to the immense growth of the congested urban areas, the quality and sustainability of the underground supply and disposal infrastructure is gaining more and more importance, which, however, hardly effects the way of their planning. The single installation of sewers and pipelines with all its disadvantages is still predominantly applied. The aim of the technical paper series at hand is to present alternatives which do not only meet the requirements of sustainable construction but which may also be of high economic benefit.

The first part deals with the current situation of pipeline installation in our cities and presents its causes and consequences. The second and third part deals with alternatives of which the second part presents "Man-accessible Utility Tunnels" and the third part is concerned with their economical aspects and alternatives to the bundled installation of pipelines beyond the utility tunnel.
 
General

An important condition for the building and development of settlement structures is the existence of reliable, properly maintainable and adaptable supply and disposal systems for transporting and distributing fluids and gases – sometimes also solids – or of electric energy, data and pictures. With their help, individual plots, settlements, suburbs or regional areas are opened up or connected with each other and integrated into overall supply and disposal systems, called line networks in the following. Depending on the materials or media to be transported, one distinguishes between pipe and cable systems [1, 2].
All the line systems shown in Figure 1 are usually accommodated individually in the body of the road divided into position and depth according to standards (Figure 2).
The type, number and distribution of the lines situated in the cross section of the road are primarily dependent on the local conditions such as the width of the road, drainage method, adjacent owner and building development.
This conventional arrangement of supply and disposal lines in the cross section of the road and the separated responsibilities for the individual networks have not changed in principle for the last century. This has caused many problems in the past which still persist today. In recognition of this fact, this form of planning as well as the building, operation and servicing of the supply and disposal networks are critical factors in achieving the aims of sustainable master plans.
According to forecasts, the population of the mega cities (a term coined by the UN to describe cities with at least 10 million inhabitants) will increase dramatically by the year 2030 so that the creation of a corresponding infrastructure is one of the most urgent tasks.
In the following, the single installation of lines is presented (Figure 2), taking its problems and consequences into account as well as the possibilities and advantages of multiple installation with the example of the man-accessible utility tunnel as a base for discussion for solving the above-mentioned tasks.
 
Single Installation of Lines – Problems and their Consequences

The single installation of lines is historically caused by the difference in the times of beginning construction of the various line networks and the consequential granting of the contractually ensured rights for the supply and discharge undertakings without considering later developments. But even for new coverage areas, alternatives are often not considered due to ignorance or incompetence.
The problems caused by separated zones due to the single installation of lines in the cross section of the road can be summarized as follows [6]:
  • Most of the underground lines form network systems, i.e. they are only fully functional as a unit. Interruptions at one point could affect whole areas.
  • The individual underground installations are subject to individually defined planning and path fundamentals. As they are laid in parallel and crosswise, contact points occur constantly. Furthermore, several installations have negative effects on each other (e.g. electric cables – communication cables – gas lines – district heating lines) so that these points of contact must be specially considered in planning.
  • The space requirement of the individual underground installations varies considerably. Wherever very large structures must be accommodated, the space for the remaining underground installations is greatly reduced. Careful coordination is therefore necessary.
  • All underground installations are complex engineering constructions. Servicing measures (inspection, repairs, renovations, renewal) as well as adaptation and restoring works are usually only possible with large technical and financial means. All these measures often cause substantial hindrances in the traffic space.
This last-mentioned problem is very topical for all cities with a long history in underground infrastructure installation, as large parts of these lines are damaged or not fully functional. The reason for this is age, the numerous internal and external demands on them which have changed over the course of their use, the wrong choice of materials as well as unprofessional planning, installation and maintenance of the line networks. Damage to supply and discharge lines does not only mean an impairment of the respective system but, depending on the medium, is in many cases a danger to the environment or the population.
The repair of damage to supply and discharge lines usually takes place with the occurrence of an acute case of damage according to the so-called fire-fighting strategy, thus, uncoordinated with other supply and discharge carriers and almost exclusively in the open-cut method of construction. In inner-urban areas, this method of construction with pipe installation and renewal in the traffic lane path and especially with relatively deeply buried sewers, is increasingly subject to political and ecological constraints as these are often accompanied by
  • noise, vibration and emission loadings from construction site work and traffic diversions,
  • impairments to parallel or crossing underground lines and above-ground structures and plantings, e.g. due to water retention measures,
  • increase in the use of energy as well as loss of turnover and working time due to traffic diversion and
  • safety risks for adjacent owners.
As experience has shown, the costs for an inner-urban sewer renewal can be more than double those of a comparably new sewer installation in an unopened development area. These increased costs are mainly caused by [7]:
  • The necessary removal of the excavation mass due to the restricted space available,
  • The construction measures necessary to maintain a flow of traffic and the significant delays in construction due to this,
  • The required opening up of the road surface and its replacement,
  • Traffic measures including signposting,
  • The erection of bridges over trenches for vehicles, pedestrians, etc.,
  • The maintenance of drainage capability for gravity and pressurized sewers as well as the properties connected to the road drainage systems.
  • The significant hindrance in executing the work due to existing supply lines which in an extreme case can go as far as having to re-install all lines already in the cross section of the road within the scope of sewer replacement measures (Figure 6).
Besides the already mentioned repairs to damage or rehabilitation of damaged or over-aged lines and pipe systems there is a new and perhaps greater problem for the inner-urban infrastructure in the field of supply and discharge for the population. This is the result of the constant change and development of society which leads to changed demands on the urban supply and discharge networks. Examples from the past and the near future in the Federal Republic of Germany are listed as follows:
  • The development of glass-fibre technology with optical fibres which replace electric cables for the transmission of data.
  • The lifting of the monopolies of the telecoms, which permits other undertakings to offer telecommunication services,
  • Future developments in long-distance data transmission (Internet, digital TV, etc.) whose effects on the cabling measures cannot be foreseen yet,
  • The change of materials for gas pipes even to plastic with the demand to remove old and polluting gas piping from the ground,
  • The conversion from emission-loaded individual oil and coal-firing of building heating to piped energy systems such as natural gas or district heating,
  • The re-utilization of large areas from industrial to dwelling and services use which make other capacity demands on the piped infrastructure.
  • The seepage or utilization of rainwater whereby the flow-off areas of the sewers are insufficiently utilized with respect to hydraulics,
  • The provision of separate water circuits for drinking and utility water as only approximately 2 % of the water use in the private sphere is used for drinking or cooking and more than 30 % is used for flushing toilets,
  • The changing behaviour of users, for instance saving of electrical energy or drinking water for which purpose adaptation, closing down and, in an extreme case, removal measures will be required.
The changed behaviour of the users can have especially grave consequences for the drinking water and sewer networks. These networks have grown historically in European cites, e.g. in Germany they have achieved almost a 100 % degree of connection. The following assumptions were, and still are, made for their planning:
  • The useful operation life for water pipes is approx. 40-60 years and for sewers it is 50-80 (100) years.
  • The dimensioning of piping cross sections takes the expected increase in use into account.
  • The forecasts for water usage and sewage remain constant over several generations.
The existing line networks do not fulfil these requirements as they can only be operated satisfactorily in a relatively limited capacity range. Substantial increases, e.g. of the use of water, cannot be accommodated with these networks. But, on the other hand, also water saving measures or the substitution of drinking water for environmental reasons can cause substantial problems in the operation of water and sewage networks as is shown by numerous examples from Germany [8].
In the latter case, which has become the usual case in many communities today, the water supply undertaking must react to the changed situation and must carry out flushing by removing water from hydrants much more often in order to generate the necessary flow. Apart from the fact that this measure does not solve the stagnation problem of drinking water in the service and house water pipes, also the foreground ecological use is relativised if not, to the contrary, wrong, because the water saved in the household must be used in flushing the pipes. The economic usefulness for the household from the reduced utilization of waster is wasted in the increased operational use for the network, which are charged to the user again in the water rates.
It is difficult, if not impossible, to react to the resulting demands on the line networks resulting from the constant change of the development of society because of the current installation practice as short-term access to the piping is not possible and cannot be financed. This means that the supply and discharge undertakings are not in the position to
  • adapt their networks quickly and cheaply corresponding to their customer’s requirements,
  • easily react to new technical developments, and
  • to integrate new lines into the overall system.
But alternatives are available.


Bibliography

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

[2] Stein, D.: Trenchless technology for utility networks – An important part of the development of mega-cities. Proceedings of the World Tunnel Congress`98 on Tunnels and Metropolises in Sao Paulo, Brazil, April 25th-30th, 1998 (Eds.: Negro, A., Ferreira, A. A.), 1247–1254. A.A. Balkema, Rotterdam/Brookfield, 1998.

[3] DIN 1998: Unterbringung von Leitungen und Anlagen in öffentlichen Flächen, Richtlinien für die Planung (1978).

[4] www.worldbank.org/data.

[5] www.unitracc.de. Company information Feuerstein - Gazit Engineers Ltd., Israel.

[6] Girnau, G.: Unterirdischer Städtebau. Düsseldorf: Ernst & Sohn, 1970.

[7] Stein, D.: Instandhaltung von Kanalisationen. 3rd edition, Berlin: Ernst & Sohn, 1998.

[8] Stein, D.: Erneuerung innerstädtischer Ver- und Entsorgungsleitungen durch Leitungsgänge. In: D. Stein (ed.), Der begehbare Leitungsgang, Beiträge zur Kanalisationstechnik, Vol. I, Berlin: Analytika, 1990, 9-24.
 
To read Part II of this article series, please click here.
To read Part III of this article series, please click here.

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