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close this bookWater Manual for Refugee Situations (UNHCR, 1992, 160 p.)
close this folder10. Water distribution systems
View the document(introduction...)
View the documentGeneral
View the documentTypes of pipeline systems
View the documentValves and taps
View the documentOther system components
View the documentConsiderations for pipeline designs
View the documentPipeline construction

Pipeline construction

18. Beneficiaries, not taking into account strangers, heavy animals or vehicles, may cause considerable damage to exposed pumping equipment, pipes or fittings with frustrating results. These problems should be prevented by taking practical and tailor-made steps for each project. In this context, efforts should be undertaken to make beneficiaries understand the difficulties of repairing damaged systems and the negative impact that such repairs have on their own welfare; their cooperation in protecting the system should, therefore, be fostered and encouraged.

19. The design and construction of a water supply system should be guided by the need to avoid these problems and to provide maximum protection to the whole system against adverse weather and other environmental conditions. If pipelines are not constructed properly the first time, remedial actions are difficult, time consuming and discouraging tasks, especially if they have to be undertaken as a result of carelessness or sloppy construction techniques or practices.

20. Pipes should normally be laid within trenches to protect them from damage from traffic or weather conditions. In the tropics, the proper depth of trenches should be at least 0.80 metres; deeper trenches are necessary to avoid freezing and other cold weather effects in higher latitude countries; local experience should therefore be taken into account in choosing the right depth of trenches, always bearing in mind the increased costs deeper trenches represent. Although there are no special requirements for the width of trenches, cost factors determine that this width should be kept to the minimum necessary (mainly determined by the width of the trenching equipment). The trench should be dug in sections equal to the length of the pipe to be buried in it each day and should be free of sharp rocks or bends that may interfere with the pipe; when the entire section is dug, it should be inspected before the pipe is laid.

21. Once the pipe is laid within the trench, and all connections inspected, backfilling may be carried out. The material to be used should be soft and granular; large stones should be avoided. An initial backfilling, to cover the pipes with a minimum of 20 cm. of soil, should be carried out as soon as possible after the pipe has been laid into the trench to provide protection to the pipe. Final backfilling may be carried out after the entire pipeline section has been tested.

22. Although the pipeline should, ideally, follow the route that was originally surveyed and used in the pipeline design and related calculations, it may be necessary during construction activities to introduce some detours or other changes to avoid impassable areas (rocky terrain, landslides, deep gullies) not identified by the original survey. In this case, these detours must be re-surveyed to determine how will they affect the overall hydraulic behaviour of the pipeline system and to calculate additional requirements (pipes, construction materials, other structures, etc.).

23. It is always worthwhile remembering that, within relatively short periods, visible traces of buried pipelines may disappear, making it difficult, and sometimes costly, to find a pipe trace. Permanent markers, at strategically located reference points should be used for future reference. Concrete pegs are the most commonly used markers. They should be located at all branch points, reducers, changes in pipeline direction and at regular intervals in open terrain or bush. A record of each marker, containing at least information on pipeline materials, diameters and direction of pipes should be kept at hand.

24. Leaks or damages to the pipeline should be identified before the final backfilling of the trenches is undertaken. Test pressures should be the maximum pressures possible if the system is gravity fed, or at least 20% higher than the working pressure of pumping mains. The test should be carried out continuously for at least 15 minutes for each 100 metres of pipeline; the air at all high points must be released during the filling of the pipeline, before the testing.