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of about 1 in 40 could be maintained on connections if the invert level of the main sewer was at least 500 mm below ground level. Some reduction in invert depths would be possible if the floor levels of sanitation blocks were raised more than about 150 mm above the lane level but 500 mm depth to sewer invert was adopted as the minimum standard for the scheme. The same standard was adopted for the North-east Lahore project for lanes of 3 m width and under on the basis that vehicle loads would not be a problem and that surveys had shown that most sanitation facilities were located close to the front of plots. Lanes in Faisalabad are generally rather wider, typically 5 m or more, and are accessible to some vehicles. There has been some debate on what the minimum cover should be in these circumstances but the evidence suggests that pipes can take at least moderate traffic loads at covers of about 250 mm. The standards given in Table 4.1 are those suggested by Tayler and Cotton (1993) based on the North-east Lahore experience. |
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The sewers in the Peshawar Cantonment schemes are laid in narrow lanes, typically less than 1.5 metres wide, where there is no possibility of any traffic loading. In these lanes, locally made plastic pipes have been laid with covers of about 150 mm. More research is needed to determine standards for the cover to be provided over plastic pipes in locations were vehicle loads can be expected. |
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Clay pipes are not used in Pakistan but are not uncommon in India. A British clay pipe manufacturer (Naylor Bros (Claywares) Ltd, Barnsley. 1982) suggests the minimum covers shown in Table 4.2. Extra-strength pipes are supplied as standard in the UK but caution is needed as the pipes used in India are not of the same quality as those produced in Britain. As for locally |
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| | Street width | | | | < 3 m | | | | 34.5 m | | | | 4.56 m | | Cars, horse drawn carts, small trucks |
| | | > 6 m residential | | |
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