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efforts to reduce standards have been resisted by government agencies in many countries, largely it seems because they equate reduced standards with second-rate standards. A more promising approach is to start from the premise that standards should be appropriate, recognizing that they should be framed in relation to the location of a facility and the function which it is intended to perform. The consequences for various aspects of sewerage are discussed below. |
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4.2.1
Minimum Sewer Depth |
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Shallow sewers, expecially those which are less than about 1.2 m deep, can be significantly cheaper than deeper sewers. Where labour costs are low, this is not primarily because of any saving in excavation costs but rather because access to shallow sewers for cleaning and maintenance purposes can be gained through inspection chambers which do not require man entry and can thus be much smaller than conventional manholes. The depth of a sewer at any point along its length is affected by its depth at its head and the subsequent gradients. Thus the minimum allowable sewer depth and minimum sewer gradients are important determinants of the cost of a sewerage scheme |
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All the projects from Pakistan described in this chapter, apart from the Peshawar Cantonment Busti schemes use locally produced concrete sewer pipes. At the time that proposals for Yusufabad were being developed, it was clear that these pipes could take fairly high loads. At one point on the access road to the scheme, a 300 mm pipe was used as a culvert to carry wastewater from an existing artesian installation under the road. Although the cover on this pipe was minimal, not more than about 150 mm, and the road was unsurfaced, the pipe had suffered no damage from occasional traffic, including some loaded trucks. In view of this, it seemed reasonable to assume that, from a structural point of view, pipes could be laid with minimal cover in the narrow lanes of the housing scheme which would not be accessible to heavy traffic. |
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The other factor was the depth required to ensure that house connections could be made to the sewer at a reasonable slope. The toilet and bathroom facilities of the core housing units were located at the front of the plots and it was found that gradients |
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