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In the design of access ramps, the direction is normally specified to be sloping down towards downstream so as to avoid the occurrence of over-shooting of flowing water for supercritical flow in case of aligning the ramps in the reverse direction of channel flow.
Flow around a bend results in a rise of water surface on the outside of the bend and it is natural to consider that extra height of channel wall on the outside of bend to prevent overflow of water.
The joints for box culverts and channels should be capable of accommodating movements arising from temperature and moisture changes. However, the joints are not necessarily designed as watertight except the following conditions:
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In the life cycle of a concrete structure (not prestressed concrete), it will generally undergo the following process of contraction and expansion:
Contraction:
(a) Early thermal movement
(b) Seasonal contraction owing to drop in temperature
(c) Shrinkage
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Both road gullies and catchpits are the two basic types of drainage inlets of drainage system. Though they are designed to catch stormwater, road gullies and catchpits are intended to catch stormwater at different locations.
For pipe size < 300mm, rodding is usually adopted in which workers place about 1m long rods through the pipes to the location of blockage and manually operate the rod to clear the blockage. For pipe size < 700mm, water-jetting is normally employed in which water is supplied from nearby fire hydrants and pressurized water jet is used for clearing blockage. Read More
Traditionally, manholes covers are made of cast iron. However, in the viewpoint of pipe maintenance, frequent opening of manhole covers has to be carried out. Therefore, it poses potential safety hazard to the workers during the lifting-up process of manhole covers because cast iron manhole covers are very heavy to normal workers. Consequently, research has been conducted and ductile iron is considered as a better choice than cast iron because it can resist the same traffic loads with lower self-weight. Moreover, as ductile iron is less brittle than cast iron, the traditional cast iron manhole covers are more susceptible to damage and thus requires higher maintenance cost.
In some countries, manhole covers are designed into split triangular shapes to reduce the effect of rocking from traffic. However, the two pieces of triangular covers should be bolted together. As for a piece of triangular cover, it is easily dropped into the rectangular hole of manhole during routine maintenance. Therefore, from maintenance point of view, some countries prefer another geometrical shape i.e. circular, as this is the only shape that the cover could hardly be accidentally dropped into the manhole.
