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Figure 4.3
Deep manholes in Pakistan: standard design (left) and
a recommended modification (right) |
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tice. This is a departure from the normal practice in Pakistan which is to corbel in the upper manhole walls, as shown in Figure 4.3, so as to allow a cover to be fitted without a reinforced roof slab. A similar detail is shown on standard drawings of the Maharastra Housing and Development Authority (MHADA) and is probably widespread in India. While it is economical from a construction point of view, it appears not to meet the criterion that standards should relate to practice as sewer workers need to be accomplished rock climbers to descend the step irons which disappear out of view below the overhang. At first sight, it would appear that a better option would be to keep one side of the manhole vertical, corbelling the other side of the manhole over as shown in Figure 4.3. However, investigation suggests that the normal practice in Faisalabad is to lower a sewer man on a rope rather than to use the step-irons, which are often badly corroded. It is arguable that this practice, while far from ideal, is the best option available in the circumstances. |
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No step irons have been provided in any of the smaller chambers provided in the Pakistani schemes. A previous design recommendation (Tayler and Cotton, 1993) suggested that the plan dimensions of chambers intended for depths to invert between 1000 and 1350 mm should be increased to 1000 × 600 mm to |
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