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:

(i) There is a high possibility of occurrence of high water table in the vicinity of box culverts/channels. The high groundwater level and rainwater seepage through embankment may cause water passing through the joints and washing in soils. Consequently, the loss of soils may lead to the failure of the structures.

(ii) If the box culvert/channels are designed in such a way that water flow through joints from the structures causes the washing out of bedding materials, the requirement of watertightness of joint has to be fulfilled.

(iii) In cold countries, road salt is sometimes applied on roads above box culvert or at crossings of channels to prevent freezing and thawing. The leaching of road salts into the joints may cause corrosion of joint reinforcement.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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

Expansion:
(a) Seasonal expansion owing to drop in temperature

The order of magnitude for items (a) to (c) is more or less the same. Hence, qualitatively speaking, for a given length of concrete structure, the number of contraction joints should be more than the number of expansion joints and they are roughly in the order of 3:1 to 2:1 based on the number of expansion and contraction process above. Of course, the actual spacing and number of contraction joints and expansion joints should be determined case by case.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

Precast concrete manholes are normally constructed by placing the bases of manholes firstly. The walls of precast manholes are formed by placing the precast concrete rings one on top of the other up to the required height. Someone may notice that reinforcement used for resisting the lateral earth pressure and surface loads are not considered in some design. It is discussed in Concrete Pipe Association of Great Britain that analysis of soil pressures shows that standard unreinforced precast units are capable of resisting uniformly distributed pressures (e.g. loading condition in a manhole) down to a depth of 150m. If very severe road traffic and side loads are encountered, an additional concrete surround of about 150mm may be provided.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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.

Catchpits are designed to receive stormwater from slopes and stream courses. There is no standard design of catchpits and they can take different forms and shapes like inclusion of sand trap to improve the quality of collected stormwater and to prevent the blockage of drains. On the other hand, road gullies are intended to receive stormwater from roads only.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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.

Winching method is adopted for all sizes of pipes.

For instance, for pipe size exceeding 1050mm, it is stated in Stormwater Drainage Manual that maximum intervals between manholes along straight lengths should be 120m. This is because for sizes over 1050m, the main method of pipe maintenance is by winching whose maximum length of operation is 120m. Similarly, the maximum intervals of manholes for other straight pipes are derived from their corresponding maintenance methods.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.