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produced in rapidly rotating horizontal moulds, using the same process as that used in the larger casting yards. The reinforcement used is nominal and does not comply with the BS and ASTM standards used by the larger casting yards. The internal surface of pipes inspected at a small casting yard in Faisalabad was rather uneven and this might increase the roughness slightly over that normally assumed in hydraulic calculations. Joints are made by inserting a strip of jute soaked in cement slurry into the gap between the pipes and then surrounding the whole joint in sandcement mortar. |
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The use of plain-ended pipes is not in accordance with government specifications, but experience in Yusufabad and the FAUP suggests that sewers built in this way perform perfectly satisfactorily. This is significant, given that the price of plain-ended pipes is about one-third of that of those with sockets. |
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Clay pipes used in India are also of the spigot-and-socket type, as are the locally made plastic pipes and fittings which are available in Pakistan and no doubt elsewhere. Joints in the latter are normally made to allow a push fit and this is perfectly satisfactory for the small diameters required for branch sewers in interceptor tank systems. |
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Sewers in Yusufabad were laid in trenches in previously undisturbed fine-grained soil which provided ideal conditions. Pipes were laid directly on to the trench bottom. The common practice in informal areas in Lahore is to raise house plinth levels some way, typically about 11.5 m, above the natural ground level, and it is not uncommon for solid waste to be used to bring lane levels up to the required height. Thus the ground condidions are rather variable and unreliable. All sewers in the North-east Lahore scheme were laid on a 100 mm brick ballast bed, brick being used because the nearest source of stone was over 100 km away. Bedding is required by Pakistan Government specifications, as it was for the World Bank-funded schemes in India. The early community-managed sewer projects implemented under the FAUP have not included bedding and this is one among several examples of where government procedures and those adopted by local communities are likely to be in conflict. |
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