A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
hydrogen sulfide. Moreover, it is reported to be unaffected by the presence
of solvents.
However, there are still some chemicals which are known to cause damage
to vitrified clay pipe. For instance, vitrified clay pipe is not immune to attack
by hydrofluoric acid and hot concentrated caustic wastes.
4. Do extreme temperatures damage vitrified clay pipes? (S2)
Vitrified clay pipe is capable of withstanding extreme temperatures.
However, vitrified clay pipe is liable to damage by thermal shock – a swift
change of temperature. Such rapid temperature variation induces thermal
gradients inside the pipe wall which produces stresses which damage the
pipe. To guard against possible damage of vitrified clay pipe by thermal
shock, engineers should check in design about the temperature of sewage
to be carried, rate of flow, temperature of pipe and soils and the wall
thickness of clay pipes.
5. What are the effects of sediment deposition in sewers? (DS1)
There are mainly three major effects of sediment deposition in sewers:
(i) The deposited sediment may cause initiate small blockage of flow.
Later when larger solid builds up it may result in total blockage of
sewers.
(ii) The deposited sewer restricts flows leading to the drop in hydraulic
capacity.
(iii) The deposited sediment serves as a point of pollutant storage or
generator. The pollutants are stored temporarily and be discharged
in high flow conditions. Moreover, biomedical change in sediment
deposition releases gases which are corrosive to sewers.
6. What are the limitations of CCTV regarding the inspection of
sewers?
CCTV is a well-established and prevalent method for pipe inspection.
However, there are several limitations of CCTV technology:
(i) It could only provide the view of pipe internal surface above
waterline.
(ii) It does not provide the view of soil conditions surrounding the pipe.
(iii) Most CCTV system is incapable of measuring pipe gradient.
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